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Magnetic Property
Measurement System
AC Option User's ManualPart Number 1017-llOA

Quantum Design
11578 Sorrento Valley Rd.
San Diego, CA 92121-1311
USA(858) 481-4400
Technical support(800) 289-6996(858) 481-7410
Fax
Second edition of manual completed November 1999.

Trademarks
All product and company names appearing in this manual are trademarks or registered trademarks of their respective holders.

U.S. Patents
4,791,788 Method for Obtaining Improved Temperature Regulation When Using Liquid Helium Cooling
4,848,093 Apparatus and Method for Regulating Temperature in a Cryogenic Test Chamber
5,053,834 High Symmetry DC Squid System5, 110, 034 Superconducting Bonds for Thin Film Devices
5, 139, 192 Superconducting Bonds for Thin Film Devices
5,311,125 Magnetic Property Characterization System Employing a Single Sensing Coil Arrangement to Measure AC
Susceptibility and DC Moment of a Sample (patent licensed from Lakeshore)
5,319,307 Geometrically and Electrically Balanced DC Squid System Having a Pair of Intersecting Slits
5,647,228 Apparatus and Method for Regulating Temperature in Cryogenic Test Chamber

Foreign Patents
U.K.
CanadaJapan

9713380.5 Apparatus and Method for Regulating Temperature in Cryogenic Test Chamber
2,089,181 High Symmetry DC Squid System
2,533,428 High Symmetry DC Squid System

C 0

N T E N T S

Table of Contents
PREFACE
Contents and Conventions ............................................................................................................................... vii
P.1 Introduction ...................... ~ ................................................................................................................................ vii
P .2 Scope of the Manual. ......................................................................................................................................... vii
P.3 Contents oftheManual ..................................................................................................................................... vii
P .4 Conventions in the Manual .............................................................................................................................. viii

CHAPTERl
Introduction to the AC Option ...................................................................................................................... 1-1
1.1 Introduction ...................................................................................................................................................... 1-1
1.2 Overview of the AC Option ............................................................................................................................. 1-1
1.2.1 Advantages of the MPMS AC System ...................................................................................................... 1-1
1.2.2 MeasurementRange .................................................................................................................................. 1-2
1.3 Overview of the AC Option Electronics .......................................................................................................... 1-3
1.3.1 AC Drive System ....................................................................................................................................... 1-3
1.3.2 AC Digitizer .............................................................................................................................................. 1-3
1.4 Overview of System Software .......................................................................................................................... 1-4

CHAPTER2
AC Susceptibility Measurement ................................................................................................................... 2-1
2.1 Introduction ...................................................................................................................................................... 2- l
2.2 Overview of AC Susceptibility Measurements ................................................................................................2-1
2.3 Measuring AC Susceptibility ........................................................................................................................... 2-2
2.3.l Attach the Sample ..................................................................................................................................... 2-2
2.3.2 Insert the Sample ....................................................................................................................................... 2-3
2.3.2.1 Vent the Airlock Space ....................................................................................................................... 2-3
2.3.2.2 Lower the Sample Rod into the Airlock Space .................................................................................. 2-4
2 .3 .2 .3 Purge the Airlock Space ..................................................................................................................... 2-5
2.3.2.4 Lower the Sample Rod into the Sample Chamber ............................................................................. 2-5
2.3.3 Confirm the Sample Installation and Define the Sample Parameters ........................................................ 2-6
2.3.4 Center the Sample ..................................................................................................................................... 2-7
2.3.4.1 Initialize the Sample Transport .......................................................................................................... 2-7
2.3.4.2 Define the Parameters ......................................................................................................................... 2-8
2.3.4.3 Run the Centering Measurement ...................................................................................................... 2-10
2.3.4.4 Adjust the Sample Position .............................................................................................................. 2-11

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Table of Contents

2.3 .5 Measure the Sample ................................................................................................................................ 2-11
2.3.5.1 Define the Parameters ....................................................................................................................... 2-13
2.3 .5 .2 Select the Data Files ........................................................................................................................ .2-14
2.3.5.3 Run the Measurement ....................................................................................................................... 2-15
2.3.5.4 Aborting a Measurement .................................................................................................................. 2-15
2.3.5.5 Viewing the Data Files ..................................................................................................................... 2-15
2.4 Description of the AC Measurement Process ................................................................................................. 2-16
2.5 Description of Signal Nulling ......................................................................................................................... 2-17
2.5 .1 DC Offset Nulling ................................................................................................................................... 2-17
2.5.2 Line Nulling ............................................................................................................................................ 2-l 7
2.5.3 Drive Nulling ........................................................................................................................................... 2-18

CHAPTER3
AC System Calibration .................................................................................................................................... 3-l
3 .1 Introduction ...................................................................................................................................................... 3-1
3 .2 Overview of Calibration .................................................................................................................................. .3-1
3.3 Instrument Response Calibration ..................................................................................................................... 3-1
3.4 Absolute Calibration........................................................................................................................................ .3-3

CHAPTER4
AC Sequence Commands ............................................................................................................................... .4-l
4 .1 Introduction ..................................................................................................................................................... .4-1
4.2 Description of AC Sequence Commands ......................................................................................................... 4-1
4.2. l AC Center and Measure Sequence Commands ........................................................................................ .4-1
4.2.1.l AC Center .......................................................................................................................................... .4-l
4.2.1.2 AC Parameters ................................................................................................................................... .4-2
4.2.1.3 Measure AC ....................................................................................................................................... .4-2
4.2.1.4 Scan AC Amplitude ............................................................................................................................ 4-3
4.2.1.5 Scan AC Frequency ........................................................................................................................... .4-4
4.2.2 AC Calibration Factor Sequence Commands ........................................................................................... .4-5
4.2.2.1 Current to Flux .................................................................................................................................. .4-5
4.2.2.2 Drive Resolution ................................................................................................................................ .4-5
4.2.2.3 Null Resolution .................................................................................................................................. .4-5
4.2.2.4 Regression ......................................................................................................................................... .4-5
4.2.3 AC Diagnostic Sequence Commands ....................................................................................................... .4-6
4.2.3.1 AC ClockFrequency .......................................................................................................................... 4-6
4.2.3.2 AC Filter ............................................................................................................................................ .4-6
4.2.3.3 Amplifier Gain .................................................................................................................................. .4-6
4.2.3.4 Amplitude .......................................................................................................................................... .4-6
4.2.3.5 Apply Nulling .................................................................................................................................... .4-7
4.2.3.6 Null DC Offset .................................................................................................................................. .4-7
4.2.3. 7 Null Line Noise .................................................................................................................................. 4-7
4.2.3.8 Signal Clocking ................................................................................................................................. .4-7
4.2.3.9 Steps Per Cycle ................................................................................................................................... 4-7
4.2.3.10 Two-Point Measurement ................................................................................................................. .4-7
4.2.3.11 Wave Frequency .............................................................................................................................. .4-7

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Contents
Table of Contents

CHAPTERSAC Calibration Factors and Diagnostics .................................................................................................. 5-1
5.1 Introduction ...................................................................................................................................................... 5-1
5.2 AC Calibration Factors ..................................................................................................................................... 5-1
5.3 AC Diagnostics ................................................................................................................................................ .5-3
5.3.1 AC Diagnostic Settings ............................................................................................................................ .5-4
5.3.1.1 Drive Amplitude ................................................................................................................................. 5-4
5.3.1.2 AC Filter ............................................................................................................................................. 5-4
5.3.1.3 Gain .................................................................................................................................................... 5-4
5.3.1.4 Wave Frequency ................................................................................................................................. 5-5
5.3.1.5 Clock Frequency ................................................................................................................................ 5-5
5.3.1.6 Steps Per Cycle ................................................................................................................................... 5-6
5.3.1.7 Signal Clocking .................................................................................................................................. 5-6
5.3.1.8 Two-Point Measurement .................................................................................................................... 5-6
5.3.1.9 Apply Nulling Waveform ................................................................................................................... 5-6
5.3.1.10 Write Nulling Diag ........................................................................................................................... 5-7
5.3.2 AC Diagnostic Controls ............................................................................................................................ 5-7
5 .3 .2.1 Null DC Offset ................................................................................................................................... 5-7
5.3.2.2 Null Line Noise .................................................................................................................................. 5-7

APPENDIX A
Data File Format. ............................................................................................................................................... A-1
A.1 Introduction .................................................................................................................................................... A-1
A.2 Format ofDataFiles ....................................................................................................................................... A-1
A.2.1 Data File Header ...................................................................................................................................... A-1
A.2.2 Data Section ............................................................................................................................................. A-3
A.2.2.1 Data Section Field Names ................................................................................................................ A-3
A.3 Data Types ...................................................................................................................................................... A-4
A.3.1 Numerical Data ........................................................................................................................................ A-4
A.3.2 Strings ...................................................................................................................................................... A-4
A.3.3 Boolean ......................... .-.......................................................................................................................... A-4
A.3.4 Additional Information ............................................................................................................................ A-4

References .............................................................................................................................................. References- I

Index ................................................................................................................................................................. Index-1

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Contents
Table ofFigures

FiguresFigure 2-1. Positioning the Sample in a Drinking Straw ........................................................................................... 2-2
Figure 2-2. Sample Transport and Electronics Control Assembly ............................................................................ 2-3
Figure 2-3. 0-Rings on Socket Block Assembly ...................................................................................................... 2-4
Figure 2-4. Sample Description Dialog Box ............................................................................................................. 2-6
Figure 2-5. AC Centering Dialog Box ...................................................................................................................... 2-8
Figure 2-6. AC Center Parameters Dialog Box ......................................................................................................... 2-8
Figure 2-7. Plot of AC Centering Scan Data File .................................................................................................... 2-10
Figure 2-8. AC Measurement Dialog Box .............................................................................................................. 2-13
Figure 4-1. Measure AC Dialog Box for Sequence Mode ........................................................................................ 4-2
Figure 4-2. Scan AC Amplitude Dialog Box ........................................................................................................... .4-3
Figure 4-3. Scan AC Frequency Dialog Box ........................................................................................................... .4-4
Figure 5-1. AC Group in Calibration Factors Dialog Box ....................................................................................... .5-2
Figure 5-2. AC Diagnostics Dialog Box .................................................................................................................. .5-3

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Contents
Table of Tables

TablesTable 2-1. Sample Parameters ................................................................................................................................... 2-6
Table 2-2. AC Measurement Parameters ................................................................................................................. 2-12
Tr.ble 2-3. SQUID Parameters ................................................................................................................................. 2-12
Table 5-1. AC Calibration Factors ............................................................................................................................ 5-2
Table 5-2. Clock Frequencies Used to Validate AC Calibration ............................................................................... 5-4
Table 5-3. System-Defined Clock Frequencies ........................................................................................................ .5-5

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P

R

E

F

A C E

Contents and Conventions

P.1

Introduction
This preface contains the following information:

P.2•

Section P.2 discusses the overall scope ofthe manual.

•

Section P.3 briefly summarizes thecontents of the manual.

•

Section P.4 illustrates and describes
conventions that appear in the manual.

Scope of the ManualThis manual describes the MPMS AC option and explains how to perform AC sample measurements.
MPMS MultiVu is the software application controlling the AC system. The Magnetic Property
Measurement System: MPMS MultiVu Application User's Manual discusses MPMS MultiVu in detail.

P.3

Quantum Design

Contents of the Manual•

Chapter I introduces the AC option
and discusses the AC option electronics.

•

Chapter 4 discusses the AC sequencecommands.

•

Chapter 2 explains how to perform animmediate-mode AC measurement.

•

Chapter 5 discusses the AC calibration
factors and diagnostics.

•

Chapter 3 describes the AC systemcalibration.

•

Appendix A discusses the data file format
and the information appearing in AC data
files.

MPMSACOption User's Manualvii

Preface
Contents and Conventions

Section P.4
Conventions in the Manual

P.4

Conventions in the Manual
File menu

Bold text distinguishes the names of menus, options, buttons, and panels appearing
on the PC monitor.

File>OpenThe > symbol indicates that you select multiple, nested software options.

. dat

The Courier font distinguishes code and the names of files and directories .

<Enter>Angle brackets distinguish the names of keys located on the PC keyboard.

<Alt+Enter>

A plus sign connecting the names of two or more keys distinguishes keys you press
simultaneously.
A pointing hand introduces a supplementary note.
An exclamation point inside an inverted triangle introduces a cautionarynote.
A lightning bolt inside an inverted triangle introduces a warning.

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CHAPTER

1Introduction to the AC Option

1.1

Introduction
This chapter contains the following information:

1.2•

Section 1.2 presents an overview of theAC option.

•

Section 1.3 presents an overview of theAC electronics.

•

Section 1.4 presents an overview of the
MPMS MultiVu application.

Overview of the AC Option
In an AC susceptometer, an oscillating AC magnetic field is applied to the sample. The change in flux
seen by the detection circuitry is caused only by the changing magnetic moment of the sample as it
responds to the applied AC field. The differential or AC susceptibility ofXac = dM!dH obtained fromthese measurements is described as having both real and imaginary components X' and X'', where theimaginary component is proportional to the energy losses in the sample. The complex susceptibility
can provide various types of information on properties such as the structural details of materials,
resonance phenomena, electrical conductivity by induced currents, relaxation processes such as flux
profiles and flux creep in superconductors, and energy exchange between magnetic spins and thelattice in paramagnetic materials.

1.2.1

Advantages of the MPMS AC System
Conventional AC susceptometers measure the voltage induced in an inductive detection coil by an
oscillating AC magnetic moment. The most common systems use mutual inductance bridges tomeasure the voltages induced, and some use digital processing to improve noise rejection. Thesesystems measure only signals with frequencies at or very near the applied excitation, so sensitivity isgreatly increased by reducing the effective noise level to that in the measurement bandwidth centeredon the frequency of interest. However, conventional systems lose sensitivity at low frequencies
because the voltage induced in the detection coil is proportional to the frequency of the oscillating
drive field.

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MPMS AC Option User's Manual

1-1Chapter I
Introduction to the AC Option

Section 1.2
Overview of the AC Option

The MPMS AC option solves this problem by combining an AC drive field with a SQUID-based
detection system. The SQUID (Superconducting QUantum Interference Device) is an extremely
sensitive flux-to-voltage converter that directly measures the change in flux as the sample moves
through a superconducting detection coil coupled to the SQUID circuit. The frequency-independent
coupling between magnetic flux and induced currents in the superconductors allows use of AC
frequencies and AC drive fields that are many orders of magnitude lower than those used inconventional AC systems.

In the MPMS AC system, a copper drive coil is used to generate the AC field in the sample chamber.
The drive coil is situated in the helium bath between the DC magnet and the gradiometer detection
coils, concentric with the MPMS DC superconducting magnet, with all three components combined
into a rigid structure to minimize changes in coil geometry as the sample temperature and DC field
are varied.
All changes to the MPMS for the AC option are in the Model 1822 MPMS Controller electronics andthe accompanying software. All operations necessary for taking AC measurements are integrated into
the MPMS MultiVu software application. The MPMS AC system automatically controls operations
during a measurement; user input is required only to initiate the measurement.

1.2.2

Measurement Range
The MPMS AC system allows AC measurements of a sample's magnetic moment with a resolutionof 5 x 10·12 A · m2 over a frequency range of 0.001-1000 Hz with loss of sensitivity occurring only at
frequencies below 0.01 Hz. The MPMS AC system operates over the temperature range of2-400 K
and in applied DC fields up to ±7 T. The system's combination of extremely high SQUID sensitivity
and the inherently high noise rejection in AC techniques offers the potential for extremely sensitive
AC susceptibility measurements on spin glasses and on other samples characterized by long relaxation
times. The MPMS AC system is also ideal for samples, such as high-temperature superconductors,
whose material characteristics or magnetic effects require very small excitation fields.

1-2

MPMSAC Option User's Manual

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Section 1.3
Overview C?fthe AC Option Electronics

Chapter 1
Introduction to the AC Option

1.3

Overview of the AC Option Electronics
In the MPMS AC system, magnetic flux from the sample is detected by a superconducting pickup coilthat is part of a closed-loop superconducting circuit inductively coupled to the SQUID. The feedback
circuitry is also coupled to this circuit through a superconducting DC flux transformer. The voltage
output from the SQUID electronics, which is proportional to the flux change in the detection coils, isdigitized by the AC digitizer and recorded in a data file. A current, proportional to the signal voltage,is created by the AC drive system. This current, along with other noise-canceling signals, can be fed
back inductively to the superconducting input circuit through the feedback flux transformer.

The master timing signal for the MPMS AC system is a 12-MHz crystal oscillator. This 12-MHz
crystal oscillator is reduced to 6 MHz to drive the analog-to-digital (AID) converter for the AC
digitizer, and is reduced again to 3 MHz before being passed to the AC drive system.

1.3.1

AC Drive System
The AC drive system contains a ripple counter that reduces the incoming 3-MHz signal into five clock
rates between 187.5 kHz and 2.861 Hz. The clock rates drive two 16-bit waveform synthesizers. One
synthesizer drives the solenoid that creates the AC field, and the other nulls both the sample signal andthe drive signal that couples to the SQUID via the gradiometer imbalance.
The synthesizers are based on a memory chip organized as an FIFO (First In, First Out) buffer. The
outputs of the FIFO are connected to a digital-to-analog (DAC) converter where the analog waveforms
are generated and sent to the appropriate coils. Both channels contain differential amplifiers, withranges ofxl and xlOO, that are switched simultaneously to give an effective resolution of23 bits.
The channels are clocked synchronously and contain the same number of points----up to a maximumof 8192 points--per output sine wave. To keep harmonics to an acceptable level, the system uses aminimum of 124 digital points for sine wave generation. When phase shifts are required between the
output of the drive and nulling channels, they are produced by numerically offsetting the digital sine
waves loaded into the FIFOs.

1.3.2

AC Digitizer
The primary component of the AC digitizer is a 12-bit AID converter that digitally samples the voltage
output of the SQUID electronics synchronous to the drive waveform synthesizer. Before being
digitized, the signal is passed through an instrumentation amplifier with gains of x l, x 10, and x 100,in addition to the range and gain settings of the SQUID electronics. The selectable 60-Hz notch filters
provide anti-aliasing and noise reduction. The filter roll-off frequencies were chosen to give small
phase shifts ofless than 3° at the maximum-intended drive :frequency for each sampling rate.
The data is stored in on-board memory and passed to a data file at the end of a measurement. The
maximum number of wave periods digitized in a given measurement is determined by the size of thedigitizer memory. A maximum of 65,535 16-bit data points can be stored on the board, thus limiting
the maximum amount of averaging that can be used per measurement. Data, recorded in blocks of two
wave periods, is transferred to the host computer. The MPMS MultiVu application adds the data fromdifferent blocks together point by point. This procedure has the effect of averaging the backgroundnoise at a given data point. The amplitude and phase of the resulting two-cycle data set are calculated
by using a regression algorithm with the known frequency as a fixed parameter. The calibrated phaseand amplitude corrections are applied to the raw data, and the in-phase and out-of-phase sample
moments can be recorded in several data files.

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MPMSAC Option User's Manual

1-3Section 1.4
Overview of System Software

1.4

Chapter 1
Introduction to the AC Option

Overview of System Software
The MPMS MultiVu software application controls and monitors the operation of the MPMS hardware
and the AC option. You select all AC commands in the MPMS MultiVu interface. Consequently,
while you work with the AC option, you can use any MPMS MultiVu function. For example, before
running an AC measurement, you can set the field or temperature, and when the measurement iscomplete, you can use multiple data-viewing formats to examine the data.
MPMS MultiVu supports manual, or immediate, tasks and automated, or sequence, tasks. You
automate tasks by running a sequence. The Magnetic Property Measurement System: MPMS MultiVu
Application User's Manual discusses sequences in detail.
AC data files and DC data files contain the identical header information but document different typesof data field information. Appendix A discusses the data file format in detail.

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MPMS AC Option User's Manual

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CHAPTER

2AC Susceptibility Measurement

2.1

Introduction
This chapter contains the following information:

2.2•

Section 2.2 presents an overview ofAC susceptibility measurements.

•

Section 2.4 describes the measurement
process.

•

Section 2.3 explains how to perform
an immediate-mode AC susceptibility
measurement.

•

Section 2.5 describes the signal-nulling
functions.

Overview of AC Susceptibility Measurements
A standard measurement of the AC susceptibility of a sample is a two-point measurement that
positions the sample in two locations within the SQUID pickup coils and, at each location, measuresthe effect of a nulling waveform on the sample's magnetic moment. This two-point measurement nulls
all spurious signals at the AC measurement frequency and allows extremely accurate measurements ofthe sample's AC susceptibility.
For the first part of the two-point measurement, the sample is positioned in the center of the bottom
SQUID pickup coil. For the second part of the two-point measurement, the sample is positioned in
the center of the two middle pickup coils. During both measurements, the MPMS AC system sends anulling waveform through the SQUID circuitry. When the sample is in the positively oriented, bottom
pickup coil, the nulling waveform is generated so that it cancels all signals, including the sample
signal. When the sample is in the two middle, negatively oriented coils, the negative polarity of thenulling waveform is identical to the polarity of the coils, so the strength of the sample signal isincreased three-fold. This increased sample signal is the signal the system measures to determine theAC susceptibility.

Quantum Design

MPMS AC Option User's Manual

2-1Chapter2
AC Susceptibility Measurement

Section 2.3
Measuring AC Susceptibility

2.3

Measuring AC Susceptibility
This section explains how you perform a manual, or immediate, AC measurement. The Magnetic
Property Measurement System: MPMS MultiVu Application User's Manual explains how you
automate measurements by running a sequence. Chapter 4 in this manual discusses the AC sequencecommands.
You can use the standard sample transport or the RSO sample transport to perform AC measurements.
This section explains how you use the standard transport. The Magnetic Property Measurement
System: Reciprocating Sample Option User's Manual explains how you use the RSO transport.

2.3.1

Attach the Sample
The type, size, and geometry of a sample determine the method you use to attach it to the sample
rod. This section explains how you use a clear plastic drinking straw to attach a sample. The straw
has minimal magnetic susceptibility and is thus a useful means of attaching a sample. The MPMS
Hardware Reference Manual describes other techniques you can use to attach a sample.
The susceptibility of the small straw segment used to hold the sample in the following procedure isapproximately 9 x 10-9 EMU in a temperature range of 100-300 K. Notice that a clear plastic straw
creates a significant background moment if the sample has an extremely small moment. Coloreddrinking straws, which can have dyes with considerable magnetic susceptibility, should never be used
to attach samples to the sample rod. Clear plastic drinking straws are available from Quantum Design.
Complete the following steps to attach the sample to the sample rod:

2-2

1.

Cut off an approximately 5-mm-long section of a clear plastic drinking straw. The cut-off
section, which is called the straw segment, must be small enough to fit inside another straw when
the two open ends of the segment are held vertically.

2.

Weigh and measure the sample. After you inse1: the sample into the sample chamber, you can
use the Sample Description dialog box to specify the mass, diameter, and length of the sample
so that these values are saved to a data file header.

3.

Place the sample inside the straw segment.
Quantum Design recommends using
phenolic tweezers to pick up and hold thesample. You can use a small amount ofApiezon M Grease to prevent the sample
from shaking or rattling inside the straw
segment.

SAMPLE•\'@STRAW SEGMENT/

4.

Hold the straw segment so that its two open
ends are vertical.

5.

Place the straw segment inside another clear
plastic drinking straw. Move the segment
Figure 2-1. Positioning the Sample in a
until it is in approximately the middle of the
Drinking Straw
length of the straw. Verify that the wallsof the straw obstruct the open ends of the segment and that the sample and segment are securely
positioned. The sample must not slip or rattle when you shake the straw.

6.

Wrap tape around the brass-colored end of the sample rod. Use enough tape so that the drinking
straw will fit snugly over the rod. Quantum Design recommends using Kapton tape.

7.

Place the end of the drinking straw over the tape on the sample rod. Use additional tape tosecurely attach the straw to the rod.

MPMS AC Option User's Manual

Quantum DesignChapter 2
AC Susceptibility Measurement

2.3.2

Section 2.3
Measuring AC Susceptibility

8.

Place a small piece of tape over the exposed end of the drinking straw. This extra piece of tapeprevents a loose sample from falling into the sample chamber.

9.

Move the slide seal plug up and down part of the sample rod to verify that the rod is welllubricated. If the plug does not move easily, apply a small amount of Apiezon H Grease to therod. Run your fingers along the length of the rod to ensure a light, even coating of grease.

Insert the Sample

2.3.2.1
1.

VENT THE AIRLOCK SPACE

Tum the airlock lever on the front of the probe's electronics control assembly (figure 2-2)
counterclockwise until it is horizontal and in the "Closed" position.
When the airlock lever is in the "Closed" position, it closes the airlock value and thus isolates
the lower portion of the sample chamber, protecting it from air flowing into the top portionof the chamber. The top portion of the chamber is called the airlock space. The MPMS vents
the airlock space when the airlock valve is closed.

AIRLOCK PLUG

SOCKET BLOCK ASSEMBLY

SLIDE SEAL CLAMPSAIRLOCK SPACE VIEW-PORTREADY LED
VENTING LED

AIRLOCK LEVER

Figure 2-2. Sample Transport and Electronics Control Assembly

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MPMS AC Option User's Manual

2-3Chapter2

Section 2.3
Measuring AC Susceptibility

AC Susceptibility Measurement

2.

Wait for the MPMS to vent the airlock space. The yellow "Venting" LED flashes on and off
while the MPMS vents the space and then remains off when the space is vented. The green"Ready" LED does not tum on.

3.

Push the two slide seal clamps so that the clamp handles face the front of the MPMS. The slide
seal clamps are on the socket block assembly (see figures 2-2 and 2-3). When the clamp handles
face the front of the MPMS, the airlock plug is unlocked and may be removed from the openingof the airlock space.

4.

Remove the airlock plug, which has an anodized, blue coating. Store the plug in a safe place.

2.3.2.2
I.

LOWER THE SAMPLE ROD INTO THE AIRLOCK SPACEVerify that three 0-rings are on top of the socket block assembly. Refer to figure 2-3 below.
If necessary, stand on a stool or small ladder to examine the top of the socket block. The large
0-ring at the mouth of the airlock space occasionally sticks to the sample rod when the rod isremoved from the sample chamber. Reinsert any missing 0-rings.
Never insert the sample rod into the sample chamber ifthe 0-rings on topof the socket block assembly are missing. The 0-rings prevent air, which
can damage the vacuum pump and freeze the sample, from pumping into
the chamber.

WARNINGSLIDE SEAL CLAMP

0-RING(VON2-006)
0-RING(VON2-015)
0-RING(VON2-006)

Figure 2-3. 0-Rings on Socket Block Assembly

2-4

2.

Move the slide seal plug down the sample rod until the plug rests just above the sample holder.

3.

Lower the sample rod into the airlock space. Look at the view port on the front of the sample
transport. You should see the sample rod.

4.

Move the slide seal plug down the sample rod i.ntil the plug rests on top of the socket blockassembly. If necessary, adjust the position of the slide seal clamps in order to correctly seat
the plug.

5.

Tum the slide seal plug until the white dot on the plug faces the front of the MPMS. When thewhite dot faces the front of the MPMS, the proper amount of gas flows through the slide seal.

6.

Push the two slide seal clamps completely outward or inward. When the handles of the clamps
do not face the front of the MPMS, the clamps lock the slide seal plug in position by forcing it
downward against the three 0-rings.

MPMS AC Option User's Manual

Quantum DesignChapter 2
AC Susceptibility Measurement

2.3.2.3

Section 2.3
Measuring AC Susceptibility

PURGE THE AIRLOCK SPACE

1.

Press the "Purge Airlock" button. The button if on the front of the probe's electronics control
assembly. When you push the button, the MPMS purges the airlock space. The MPMS cycles
through the purge sequence four times. The yellow "Venting" LED turns on during the purge.

2.

Wait for the MPMS to purge the airlock space. The green "Ready" LED turns on when the purge
is complete.
If the "Ready" LED does not tum on, the airlock space may have a leak. Missing or improperly
seated 0-rings may cause the leak. Perform the following steps to check for a leak: (1) Selectlnstrument>Chamber>Vent Sample Space to vent the sample chamber; (2) remove thesample rod when the "Venting" LED turns off; and (3) verify that the 0-rings are properly seated
and lubricated. If necessary, correctly seat and lubricate the 0-rings.

2.3.2.4

LOWER THE SAMPLE ROD INTO THE SAMPLE CHAMBER

1.

Tum the airlock lever clockwise until it is vertical and in the "Open" position. When the lever isin the "Open" position, it opens the airlock value.

2.

Lower the sample rod gently and slowly until the black slide clamp engages the actuator shoe on
top of the sample transport (see figure 2-2). The rod is now fully inserted in the sample chamber.
The knurled nut must be near the top of the sample rod or you will be unable to fully insert therod. If necessary, loosen the nut, and then move it until it is 1-2 inches from the top of the rod.

3.

Loosen the two clip screws until the screw threads are visible. The clip screws are on top of theactuator shoe. Do not remove the screws.

4.

Rotate the slide clamp so that its two curved slots hook around the clip screws. If necessary,
continue to loosen the clip screws until the slide clamp is properly seated.

5.

Tighten the clip screws. The clip screws secure the sample rod to the actuator shoe, so thesample transport can move the rod vertically.

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MPMSAC Option User's Manual

2-5Chapter 2
AC Susceptibility Measurement

Section 2.3
Measuring AC Susceptibility

2.3.3

Confirm the Sample Installation and Derme the Sample Parameters
1.

Select Sample> Description if the Sample Description dialog box is not open.
EJ-1

Sample Desc11ption

Figure 2-4. Sample Description Dialog Box

2.

Verify that the Sample Installed check box is selected. If necessary, click on the check box.

3.

Define the sample parameters if you want to save them to a new measurement data, or . dat,
file. Defining the sample parameters is optional. Do the following to define the parameters:w

MPMS MultiVu does not read the sample parameters during the measurement. However, if you want to save the parameters to a new . da t file,
you must define them before you specify the base name of the . da t fileand before you run the measurement. MPMS MultiVu saves sample
parameter data to a data file header only while creating the . da t file.

NOTE

(a)

2-6

Enter a descriptive name for the sample.
This is the name under which MPMS
MultiVu stores all information about the
sample and the measurement.

Table 2-1. Sample Parameters

ACCEPTEDVALUESDEFAULT
VALUE

Mass

0-10,000 mg

1 mg

Diameter

0-9mm

Imm

Length0-lOOmm

Imm

PARAMETER(b)Enter the sample mass, in milligrams.

(c)Enter the sample diameter, in millimeters.

(d)Enter the sample length, in millimeters.

(e)Define the sample shape, if necessary.

(f)Enter a comment in order to include
a comment in the data file header. A
comment may have up to 63 characters.

4.

Select OK. The Sample Description dialog box closes.

MPMS AC Option User's Manual

Quantum Design

Section 2.3
Measuring AC Susceptibility

Chapter 2
AC Susceptibility Measurement

2.3.4

Center the Sample
The sample must be centered in the SQUID pickup coils to ensure that it is correctly positioned
within the bottom and middle pickup coils during the subsequent AC measurement. The sample iscentered when it is within 0.05 cm of the half-way point of the system-defined, 6-cm scan length.
You may use an AC centering measurement or a DC centering measurement to center the sample. The
procedures below explain how you run an AC center.:Ug measurement. AC centering more accurately
centers the sample in preparation for AC sample measurements. AC centering also works best withhysteretic samples because it does not require a DC field in the magnet. However, AC centering ta1ces
considerably longer to complete than DC centering, and DC centering works best with samples having
strong magnetic moments an AC field cannot affect. The Magnetic Property Measurement System:
MPMS MultiVu Application User's Manual explains how you run a DC centering measurement.

w

If you use DC centering to center the sample for AC sample measurements,
specify a scan length of 6 cm and enable autoranging and autotracking. You
should also verify that a DC field is in the magnet.

NOTE

MPMS MultiVu automatically saves AC centering measurement data to the center. ac. lasts canfile. The Magnetic Property Measurement System: MPMS MultiVu Application User's Manual
discusses data files and data-viewing formats in detail.

2.3.4.1

w

INITIALIZE THE SAMPLE TRANSPORT
The transport must be initialized before an AC centering measurement is
ta1cen. The system-defined, 6-cm distance of the AC centering scan moves
the transport through the bottom and middle SQUID pickup coils only if thetransport is in the initialization position when centering begins. Movement
through the bottom and middle coils is necessary to center the sample.

NOTE

1.

Select Center>AC. The AC Centering dialog box opens (see figure 2-5 on the following page).
The Status panel at the top of the dialog box indicates both the current AC measurement status
and the EMU range and center position from the last AC measurement. The Control panel contains the centering command buttons. The function of each button is summarized to the right ofthe button.
The magnetic moment is not applicable during an AC centering measurement because thecentering measurement calculates a relative amplitude, not a DC moment.

2.

Select Initialize Transport. The MPMS initializes, or calibrates, the sample transport by firstlowering it to the lower-travel-limit switch, which is defined as zero, and then raising it until it isin a known position that is just above the limit switch. When the transport is in this known
position, it is correctly located to begin centering the sample.

If autotracking is enabled when you initialize the transport, the MPMS moves the transport to a
position that is far enough above the lower-travel-limit switch in order to allow adjustments forany shrinkage occurring in the sample rod. This position corresponds to a 0.5-cm offset when thesample chamber is at room temperature. To enable or disable autotracking, select Center>
AC> Parameters> Autotracking. Refer to section 2.3.4.2 below.

Quantum Design

MPMS AC Option User's Manual

2-7Chapter 2
AC Susceptibility Measurement

Section 2.3
Measuring AC Susceptibility

l!!liil EJ

AC Centering.Statu$-·-.-."'c:....:.,·~-~-~--~-,..,,,.,]MeasurementJ~e,.·:·-.. _· .. _-;;-

Moment I

EMU

NIA ,

~~ In 0.000125~n-lfi~@:!i~eg~1J ~rate aie'ia~~leuan~t _Parameters..... f-befin , wan ~~er~.
· ·F·,·. 11.•.".·.r;·'"· ·~~ ·----1·.---·_sci.i.f\the entir_e_le!\lllh_ _·-_ -_-_-. -_·.or··.
-' .. v·-· "'··~·• ; 1ran*l)Ort travel - -_ :··-- -' ,- .&e;ter I Pedorm .~nle!~ SC<n-M~stPo~lti()n. ~ J :e:~f:t~:JJD~~~~~~~----~--------~

Figure 2-5. AC Centering Dialog Box

2.3.4.2

I.

DEFINE THE PARAMETERS

Select Parameters in the AC Centering dialog box. The AC Center Parameters dialog box
opens. The dialog box lists the AC parameters and SQUID parameters the MPMS AC system
uses during an AC centering measurement. Tables 2-2 and 2-3 define the AC and SQUID
parameters, respectively.
All parameters used during an AC centering measurement are used for the subsequent AC sample
measurement unless new values are specified prior to running the measurement.
EJ

AC Center Parameters•,...-Acf>~rameteti•.- . .

- _ --.

-- .. .. --- -- - -- -l D~Am~ude lilj •. .· 'a;~stQA;~,agll fr __

H

,1

f

W'av~ Frequenc~ J§99:627 . •· - 'Time~_Av,erage fi·QAA9 . ~~~j

Ar@filierliam.!x1,_ .. s:J
P' AtiiqTrack~·. I
i-r~--- _.NuUAmpfitud!ij1_ e-006 . EMU r• APl>fyNl.liing;W'avefonn J_-_:_:_:____;._...:;_---------=~:..:.-~Jf~-~!ierin_g'~J::_: _,_:___r

4.c......::_:::..::.:_ _ _ •___

Figure 2-6. AC Center Parameters Dialog Box

2.

Define the amplitude, in oersted, of the AC drive signal the MPMS AC system applies to thesample. The drive amplitude may be any value from 0.0001 to 5.21893 Oe. The effective 23-bit
nature of the system allows a resolution sufficiently fine that only a negligible difference exists
between the amplitude you specify and the amplitude the system uses.

3.

Defme the frequency, in hertz, of the AC drive signal the system applies to the sample. The
wave frequency may be any value from 0. 0003 5 to 1512. I Hz, although the system is calibrated
from only 0.01 to 1000 Hz.
The wave frequency is a function of the clock frequency and the steps-per-cycle diagnostic
parameters. Both these parameters must have discrete values. Consequently, the wave frequency
the system uses may vary slightly from the wave frequency you specify. The system sets anduses the nearest available wave frequency.

2-8

MPMSACOption User's Manual

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Section 2.3
Measuring AC Susceptibility

Chapter2
AC Susceptibility Measurement

4.

Select the amplifier gain the system uses to control the gain of the input amplifier that is on the
AC digitizer card. The system uses the amplifi.~r gain you select only if autoranging is disabled.
If autoranging is enabled, the system automatically adjusts the gain whenever DC offset nulling,
line nulling, or an AC measurement is performed. To enable or disable autoranging, selectCenter> AC> Parameters> Use Autoranging. Refer to step 10.

5.

Define the maximum amplitude of the waveform the system uses to null the AC drive signal.
The magnitude of the AC drive signal determines the optimum choice for the null amplitude.

6.

Specify the number of data blocks MPMS MultiVu averages together for one measurement.
Each data block contains two complete cycles, or sine waves, of data. The maximum number ofblocks is 264 unless the memory available to store data points limits the number to some othervalue. The memory available to store data points is defined by Max Blocks= 2/S, where Sis thenumber of steps per cycle.

7.

Verify that autotracking is enabled. If necessary, click once on the Autotracking check box.
Autotracking compensates for thermal expansion and contraction in the sample rod.

w

Disable autotracking only if you are working with a sample that is very
sensitive to centering or if you are using a custom-built sample rod.
Autotracking instructs the MPMS to track and, before each measurement,
to adjust the position of the sample in order to keep the sample centeredin the pickup coils.

NOTE

8.

Enable drive nulling if you want to null the AC drive signal during the centering measurement.
Quantum Design recommends that drive nulling be disabled during centering measurements,
because centering measurements do not require the high accuracy nulling allows. Drive nullingensures very accurate measurements, but considerably lengthens the centering process.
The Apply Nulling Waveform check box enables or disables drive nulling only during centering
measurements. By default, drive nulling is enabled during sample measurements and disabledduring AC centering scans.

9.

Define the length, in seconds, of the SQUID settling time. The SQUID settling time is the timerequired, immediately after the sample moves, to allow the SQUID electronics to settle so thatthey stop reading the disruption created by the sample's movement. Longer settling times arenecessary when the DC field is large.

10.

Verify that autoranging is enabled. If necessary, click once on the Use Autoranging check box.
Autoranging allows MPMS MultiVu to change the EMU range as necessary so that the EMU
range is appropriate for the SQUID output. The EMU range is a sensitivity value that indicatesthe maximum magnetic moment the system can measure without saturating the SQUID detector.

w

The MPMS AC system can optimize the SQUID sensitivity for drive nulling
only if autoranging is enabled. If the system will null the AC drive signal
during the centering measurement, autoranging must be enabled.

NOTE

11.

Quantum Design

Select OK. The AC Center Parameters dialog box closes.

MPMS AC Option User's Manual

2-9Chapter 2
AC Susceptibility Measurement

Section2.3
Measuring AC Susceptibility

2.3.4.3
1.

RUN THE CENTERING MEASUREMENT

Select Center in the AC Centering dialog box. The centering measurement begins. MPMS
MultiVu takes 41 measurements of the absolute magnitude of the sample's response to the AC
drive signal. The measurements are evenly spaced over a fixed distance of 6 cm. MPMS
MultiVu takes the first measurement while the sample transport is in the initialization position.
Then as the transport moves upward, MPMS MultiVu takes 40 additional measurements. If drive
nulling is enabled, the system nulls only the fir~t measurement. Status messages at the top of the
AC Centering dialog box identify each task the system performs.
MPMS MultiVu saves all data from the centering measurement to the centering scan data, or
center. ac. last scan, file. When the centering measurement is complete, the file opens as
a graph that plots the SQUID's voltage response against the length of the scan (see figure 2-7).
As soon as the centering measurement is complete, the AC Centering dialog box displays the
new center position.
You may abort an AC centering measurement at any time by selecting the Abort button that is
at the bottom of the AC Centering dialog box.

2.

Examine the plot of the center. ac. lasts can file to determine whether the sample iscentered in the SQUID pickup coils. The sample is centered when the peak of the large, middle
curve is within 0.05 cm of the half-way point of the scan length. In the 6-cm AC centering scan,
the sample is centered when the peak of the middle curve is within 0.05 cm of the 3-cm point.
The shape of the plot is a function of the geometry of the pickup coils. The coils are wound in asecond-derivative configuration in which the single-tum, positively oriented top and bottom coils
are counterwound with respect to the two-tum, negatively oriented center coil. In the plot of thecenter. ac. lastscan file, the large, middle curve is the reading from the two center coils.
The smaller curve is the reading from the first coil. The response is similar to the response curvefrom a DC centering measurement.

.Graph View - center_ac.lastscan

1!!11~~_··ii----t---t---+-tt---it----t----i---i

I

7.. R>8~n(onj •Figure 2-7. Plot of AC Centering Scan Data File

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MPMSACOption User's Manual

Quantum DesignChapter 2
AC Susceptibility Measurement

2.3.4.4

Section 2.3
Measuring AC Susceptibility

ADJUST THE SAMPLE POSITION

1.

Select Adjust Position in the AC Centering dialog box only if the sample is not centered in the
SQUID pickup coils. The Adjust Sample Position dialog box opens.

2.

Specify the correct position of the sample if the computed position displayed in the Sample
Location text box is incorrect.

3.

Verify that the Perform scan after adjustment check box is selected. If necessary, click once
on the check box.

4.

Select Adjust Automatically. The MPMS adjusts the position of the sample so that the centerpeak of the SQUID's voltage response is within 0.05 cm of the half-way point of the scan length.
An AC centering measurement then runs. A plot of the center. ac. last scan file opens
when the centering measurement is complete.
If automatic adjustment is outside the limits of the transport mechanism and the RSO option is
not installed, you must manually adjust the sample position. Select Adjust Manually in the
Adjust Sample Position dialog box, and then follow the on-screen instructions.

5.

2.3.5

•

Lower the sample ifthe peak of the large, middle curve in the center. ac. lastscan file
is to the left of the half-way point of the scan length.

•

Raise the sample ifthe peak of the large, middle curve in the center. ac. lastscan file
is to the right of the half-way point of the scan length.

Select Close twice.

Measure the Sample
When you initiate an immediate-mode measurement, MPMS MultiVu measures the sample at thecurrent system conditions and does not wait for conditions to stabilize. If you want system conditions
to be stable when the measurement begins, you run the measurement in a sequence and use appropriate
sequence commands to stabilize system conditions. The Magnetic Property Measurement System:
MPMS MultiVu Application User's Manual explains how you run a sequence.
You may take a two-point or a one-point AC sample measurement. The two-point measurement is thedefault, and the procedures below explain how you perform a two-point measurement. A one-point
measurement is faster, but less accurate. To enable one-point measurements, you select Utilities>
Diagnostics> AC and disable the Two Point Measurement check box.
By default, drive nulling is always enabled during AC sample measurements.
Drive nulling allows the MPMS AC system to accurately measure the ACsusceptibility of the sample. If drive nullinf is disabled, you must enable itprior to running the measurement. Select Utilities> Diagnostics> AC andenable the Apply Nulling Waveform check box.

CAUTION

Up to four different data files store the data generated during a sample measurement. MPMS MultiVu
automatically saves measurement data to a data, or . dat, file and a scan data, or . last scan, file.
MPMS MultiVu also saves data to a diagnostic data, or . diag, file and a raw data, or . raw, file if
it is instructed to do so. Every data file storing AC measurement data or created to store AC measurement data has a . ac file extension. The Magnetic Property Measurement System: MPMS MultiVu
Application User's Manual discusses data files and data-viewing formats in detail.
Table 2-2 defines the AC measurement parameters. Table 2-3 defines the SQUID parameters.

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MPMS AC Option User's Manual

2-11Chapter 2
AC Susceptibility Measurement

Section2.3
Measuring AC Susceptibility

Table 2-2. AC Measurement Parameters
PARAMETERVALUES

DEFINITION

Drive Amplitude

Amplitude of applied AC drive signal.

0.0001-5.2189 Oe

Wave Frequency

Frequency of applied AC drive signal.

0.00035-1512.1 Hz

Amplifier Gain

Gain of input amplifier located on AC digitizer card.
User selection affects operation only if autoranging
is disabled.

xl
xlO
xlOO

Null Amplitude

Maximum amplitude of drive-nulling signal.

(Variable) EMU

Blocks to Average

Number of data blocks averaged together.

1-255

Meas. to Average

Number of measurements averaged together.

1-100

Time to Average

Length of time required to collect data. Time toaverage is determined by wave frequency andnumber of blocks to average.

(Variable) sec.

Autotracking

Automatic adjustment of sample's position to keep
sample centered in pickup coils.

EnabledDisabled

Table 2-3. SQUID Parameters
PARAMETER

DEFINITIONVALUES

Settling TimeTime required to allow SQUID electronics to settle
after sample has moved.

0-32400 sec.

Autoranging

Maximum magnetic moment system can measure
without saturating SQUID detector.

EnabledDisabled

Sections 2.3.5.1 through 2.3.5.3 summarize the steps you complete to run an AC measurement.

2-12

MPMS AC Option User's Manual

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Section 2.3
Measuring AC Susceptibility

Chapter2
AC Susceptibility Measurement

2.3.5.1

1.

DEFINE THE PARAMETERS

Select Measure> AC. The AC Measurement dialog box opens. The Status panel at the topof the dialog box indicates both the current AC measurement status and the magnetic momentand standard deviation from the last AC measurement. The Control panel lists the parameters
the MPMS AC system uses during a sample measurement and identifies which data files willstore the measurement data.
llll!Hil £1

AC Measurement'r. Status ·. ... . . . .... . . . •. . . .
:1 •· itie~inent td~T7 .·. ·.·. < ir-d~..-•.•. ~•••~.•••~...-..-~.._.,••-••• -.~..•.~. .
~ude~ ~; i 2.~.I)~· . StdDev rofiloooor+o\xr .

i Ph~
'!

•c

m" j•2.777S3()ft1l0t

StdD~v : 11:oom+oori .j~~~1t~i~fi~11!1~~;r~1
f;:c~QUID Par

ers;

.

. . ..

.i]·i.1'----::=~-...:...:..::...·....:::...::.:::::...._:.:_ ___ ~.::.~~----~: ____ .:;:::..=::.::...:::..-:...:...:•• ~-:...:i-Figure 2-8. AC Measurement Dialog Box

2.

Select the coordinate system MPMS MultiVu uses to display the measurement data. Data may
be displayed in the amplitude and phase coordinate system or the m' and m" (in-phase andquadrature) coordinate system.

3.

Define the amplitude, in oersted, of the AC drive signal the MPMS AC system applies to thesample. The drive amplitude may be any value from 0.0001 to 5.21893 Oe. The effective 23-bit
nature of the system allows a resolution sufficiently fine that only a negligible difference exists
between the amplitude you specify and the am:i:litude the system uses.

4.

Define the frequency, in hertz, of the AC drive signal the system applies to the sample. The
wave frequency may be any value from 0.00035 to 1512.1 Hz, although the system is calibrated
from only 0.01 to 1000 Hz.
The wave frequency is a function of the clock frequency and the steps-per-cycle diagnostic
parameters. Both these parameters must have discrete values. Consequently, the wave frequency
the system uses may vary slightly from the wave frequency you specify. The system sets anduses the nearest available wave frequency.

Quantum Design

5.

Select the amplifier gain the system uses to control the gain of the input amplifier that is on the
AC digitizer card. The system uses the amplifier gain you select only if autoranging is disabled.
If autoranging is enabled, the system automatically adjusts the gain whenever DC offset nulling,
line nulling, or an AC measurement is performed.

6.

Define the maximum amplitude of the waveform the system uses to null the AC drive signal.
The magnitude of the AC drive signal determines the optimum choice for the null amplitude.

MPMS AC Option User's Manual

2-13Chapter2

Section 2.3
Measuring AC Susceptibility

AC Susceptibility Measurement

7.

Specify the number of data blocks MPMS MultiVu averages together for one measurement.
Each data block contains two complete cycles, or sine waves, of data. The maximum number ofblocks is 264 unless the memory available to store data points limits the number to some othervalue. The memory available to store data points is defined by Max Blocks= 2/S, where Sis thenumber of steps per cycle.

8.

Specify the number of individual, two-point measurements MPMS MultiVu averages together tocompute a final measurement value. MPMS MultiVu may average together up to 100 two-point
measurements.

9.

Verify that autotracking is enabled. If necessary, click once on the Autotracking check box.
Autotracking compensates for thermal expansion and contraction in the sample rod.

1(§

Disable autotracking only if you are working with a sample that is very
sensitive to centering or if you are using a custom-built sample rod.
Autotracking instructs the MPMS to track and, before each measurement,
to adjust the position of the sample in order to keep the sample centeredin the pickup coils.

NOTE

10.

Define the length, in seconds, of the SQUID settling time. The SQUID settling time is the timerequired, immediately after the sample moves, to allow the SQUID electronics to settle so thatthey stop reading the disruption created by the sample's movement. Longer settling times arenecessary when the DC field is large.

11.

Verify that autoranging is enabled. If necessary, click once on the Use Autoranging check box.
Autoranging allows MPMS MultiVu to change the EMU range as necessary so that the EMU
range is appropriate for the SQUID output. The EMU range is a sensitivity value that indicatesthe maximum magnetic moment the system can measure without saturating the SQUID detector.

1(§

The MPMS AC system can optimize the SQUID sensitivity for drive nulling
only if autoranging is enabled. If the system will null the AC drive signal
during the centering measurement, autoranging must be enabled.

NOTE

2.3.5.2
1.

SELECT THE DATA FILES

Select Change in the AC Measurement dialog box if you want to save measurement data to a
file other than the measurement data, or . da t, file currently selected to store immediate-mode
measurement data. The name of the selected . da t file appears in the Data File panel, whichis to the left of the Change button.
Change opens the Select or Enter a New AC Data File dialog box. You can select a file andthen select Open, or you can enter the base name of a file in the File name text box, and thenselect Open.
You must create a new . da t file if you want to save the sample parameter data you enteredin section 2.3.3 to a . dat file. MPMS MultiVu saves sample parameter data to a data fileheader only while creating the . dat file. Consequently, there may not be an existing data filecontaining sample parameter data identifying your sample. If you want to append data to an
existing . da t file, try to select a file whose header information identifies your sample.

2-14

2.

Verify that the Include Diagnostic Data check box is selected if you want to save diagnostic
measurement data to a diagnostic data file. If necessary, click once on the check box.

3.

Verify that the Include Raw Data check box is selected if you want to save raw measurement
data to a raw data file. If necessary, click once on the check box.

MPMS AC Option User's Manual

Quantum DesignChapter 2
AC Susceptibility Measurement

2.3.5.3

Section 2.3
Measuring AC Susceptibility

RUN THE MEASUREMENT

To run the measurement, select Measure in the AC Measurement dialog box. The two-point measurement begins. The transport positions the sample in the center of the bottom SQUID pickup coil.
While the sample is in the bottom coil, the MPMS AC system applies the nulling waveform thatcancels all signals. Then the transport positions the sample in the center of the two middle pickup
coils. The system again applies the nulling waveform, which now, because of the reverse polarityof the middle coils, increases the sample signal so that the system can more accurately measure thesample's AC susceptibility. Status messages at the top of the AC Measurement dialog box identify
each task the system performs. Section 2.4 describes the measurement process in more detail.
When the sample measurement is complete, the AC Measurement dialog box displays the new
amplitude and phase or m' and m" coordinates and the new standard deviation.

2.3.5.4

ABORTING A MEASUREMENT

You may abort an AC susceptibility measurement at any time by selecting the Abort button thatis at the bottom of the AC Measurement dialog box. MPMS MultiVu collects all available data fromthe aborted measurement and stores the data in the active data files.

2.3.5.5

VIEWING THE DATA FILES

You select the View button located near the bottom of the AC Measurement dialog box in order toopen any data file that is selected to store the immediate-mode measurement data. View opens the
Select a Data File dialog box. By default, the dialog box lists the names of only the files that areeither actively storing measurement data or that will store data the next time a measurement runs. The
files share the identical base name. When you select a data file, and then select the Open button, thegraph view of the data file opens.
You may use the Measure> AC> View option to open a new data file that does not yet store
immediate-mode measurement data. If you specify a new base file name and then select the View
button, MPMS MultiVu creates the . dat file and the file's associated . lastscan file. MPMS
MultiVu also creates the . diag and . raw files if you have selected the Include Diagnostics Dataand Include Raw Data check boxes. All the new files are blank; they contain only the header
information, which defines the default graph format. Once you open a new file, you can modify thedefault graph format. New files remain blank until you run a measurement.
The graph view of any AC data file plots the last waveform response read from the Model 1822
MPMS Controller. The last waveform response is th~ average of all individual, two-point
measurements taken during a single sample measurement.

Quantum Design

MPMS AC Option User's Manual

2-15Chapter 2
AC Susceptibility Measurement

Section 2.4
Description of the AC Measurement Process

2.4

Description of the AC Measurement Process
A standard measurement of the AC susceptibility of a sample is a two-point measurement. The firstpart of the measurement nulls all AC signals, including the sample signal and the signal generated by
the AC field coupling to the gradiometer imbalance. The second part of the measurement uses the
sample signal, which the nulling waveform now increases by three-fold, to determine the sample'sAC susceptibility.
To begin the first part of the two-point measurement, the sample transport positions the sample in thecenter of the positively oriented, bottom SQUID pickup coil, and then the system applies an oscillating
AC magnetic field to the sample. The AC SQUID response is monitored, and a nulling waveform,
which will cancel the AC response, is calculated. The nulling waveform is injected into the SQUID
feedback circuitry, and the AC SQUID response is recorded. The iterative calculation of the nulling
waveform continues until the amplitude of the wave iteration is smaller than the null amplitude level,
the regression fit is less than 0.001, or the number of iterations exceeds 20. Section 2.5.3 discusses
drive nulling in more detail.
Once drive nulling is complete, MPMS MultiVu measures, for the specified number of data blocks, theremnant signal Mb in the bottom pickup coil. MPMS MultiVu averages the result of this measurement
and saves it to the active measurement data, or ac. dat, file. The data is fit to the equation
Mb= A+Bt+M' cos(mt)+M" sin( mt),

(2.1)

where A is any remaining DC offset, B is the linear drift in the field or temperature, co is the angularfrequency of the AC drive signal, and M' and M" are proportional to that part of the in-phase andout-of-phase components that has not been completely removed from the measurement by the drivenulling procedure.
The sample transport now positions the sample in the center of the two middle, negatively oriented
pickup coils, and the second part of the two-point measurement begins. The AC drive signal andnulling waveform last used when the sample was in the bottom pickup coil are applied. The nulling
waveform still cancels the signal generated by the gradiometer imbalance. The AC signal generated
by the sample changes polarity when moved to the middle coils. The component of the nulling
waveform that nulled the sample response in the bottom coil now adds constructively to the sample
signal. The twin loops of the middle pickup coils ancl the added signal of the nulling waveform create
an AC susceptibility sine wave that has a triple amplitude.
MPMS MultiVu measures the remnant signal Mc in the middle coils. The difference between the firstand second parts of the two-point measurement is about three times the actual sample moment. The
system fits the measured data into equation 2.1. The two sets of data are of the form
(2.2)

Mb =Mf(b)+M0
Mc =Mf(c)+M0 ,where Mis the actual moment of the sample, M 0 is any residual signal caused by imperfect nulling of
the gradiometer imbalance, andf(x) is a function of position along the central axis of the gradiometer.
The functionf(x) is the normalized response function of the magnetometer to an idealized dipole atposition x. If the sample is small compared to the dimensions of the pickup coil, the sample may beapproximated as an idealized dipole; this function is determined in a separate measurement that uses
the DC superconducting magnet. Each of the components of the susceptibility is then calculated fromthe difference between the two measurements.

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Section 2.5
Description of Signal Nulling

Chapter 2
AC Susceptibility Measurement

Mc-Mb
M=N f(c)-f(b)'(2.3)

where N is an overall normalization factor for the amplitude of the moment. The sample moment isalways measured at two positions, so the residual direct coupling M 0 is the same at both positions
and is therefore removed from the data. A phase adjustment is made to correct for any instrumental
phase shifts.
This procedure constitutes one measurement of the sample moment. If the number of measurements
to average is more than one, the sample transport positions the sample in the center of the bottom
SQUID pickup coil, and the system repeats the two-point measurement. MPMS MultiVu averages theindividual measurements and determines a fmal value of the AC moment with the standard deviation.

2.5

Description of Signal Nulling
The extreme sensitivity that is possible with SQUID-based AC measurements can be achieved only if
unwanted background signals and spurious effects are reduced. The MPMS AC system, by feeding
signals into the superconducting input circuit, automatically nulls the DC offset signal and 60-Hz line
noise naturally occurring in the system as well as the applied AC drive signal seen by the gradiometer.
Nulling the DC offset, line noise, and AC drive signal allows the SQUID electronics to be set to theirmaximum sensitivity with respect to the sample's mi;gnetic moment. The nulling signals are applied
directly to the circuit connecting the gradiometer coils to the SQUID, so the sample is always exposedto the unmodified AC drive signal.
The system uses three different types of nulling: DC offset nulling, line nulling, and drive nulling.

2.5.1

DC Offset Nulling
DC offset nulling, which is the most basic type of nulling, cancels the DC offset. If unmodified, theDC offset limits the digitization resolution to approximately 5 m V, which is roughly 100 times thesystem sensitivity. To cancel the offset, the system adds a signal proportional to the offset to the othernulling signals and then sends the nulling signals to the SQUID circuitry.
DC offset nulling automatically occurs during line nulling, drive nulling, and at the beginning ofeach AC sample measurement. The Null DC Offset diagnostics command also nulls the offset.

2.5.2

Line Nulling
The 60-Hz, line-noise nulling cancels the system noise. The system typically has about 5 x 10-6 EMU
peak-to-peak undesirable line noise at 60 Hz with odd harmonics approximately one-third as large.
The line noise at the fundamental frequency alone limits the digitization resolution to 0.5-1 mV, which
is an order of magnitude higher than the SQUID noise. To cancel the line noise, the system measures
it and then applies, to the SQUID circuitry, a 60-Hz signal with the identical amplitude but with a 180°
phase shift. The line-nulling signal also cancels any residual DC offset.

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MPMS AC Option User's Manual

2-17Chapter 2
AC Susceptibility Measurement

Section 2.5
Description of Signal NullingLine nulling automatically occurs when MPMS MultiVu takes the first AC centering or AC sample
measurement after system start-up or after the Model 1822 has been reset. Repeating line nulling at
any other time is seldom necessary. You can, however, use the Null Line Noise diagnostics commandto null the noise.

2.5.3

Drive Nulling
Drive nulling cancels the signals from the AC drive signal, the gradiometer imbalance, and the sample
moment. To cancel these three signals, the system iteratively calculates a waveform that nulls the AC
drive signal seen by the gradiometer. Nulling these signals maximizes the SQUID's sensitivity to thesample moment. Drive nulling is also called "applying the nulling waveform."
The MPMS AC system performs drive nulling before taking an AC centering or sample measurement.
When the system sends a drive signal, it also calculates and sends the waveform required to null thatsignal. The system measures any remnant signal arising from an imperfect drive cancellation, and thenuses the regression factor to make necessary corrections to the in-phase and out-of-phase componentsof the nulling waveform. The system applies the corrected nulling waveform and remeasures the net
signal. The drive-nulling procedure is repeated until the amplitude of the wave iteration is smaller than
the null amplitude parameter, the regression fit is less than 0.001, or the number of iterations exceeds
20. The system usually requires three to four iterations to read a 5 x 10-8 null in a drive field of 1 G.
The nulling waveform also cancels the DC offset and any 60-Hz line noise. The nulling waveform
always cancels the DC offset, but cancels line noise only when line noise is present. Line noise ispresent when the system takes the first AC centering or sample measurement after system start-up
or after the Model 1822 has been reset.
Drive nulling can reduce the residual AC signal in the SQUID detection system by four orders ofmagnitude, providing a total rejection of the AC drive signal of 1partin107• This factor of 10,000
improvement can be achieved by using readily available precision electronic components. However,for the system to maintain such a high rejection level, the geometric stability of the drive and detection
coils must be stable to the level ofrejection desired. The system's design creates this stability bymaking the AC drive coil an integral part of the superconducting DC magnet and by then combining
the magnet and detection coils into a completely monolithic structure. All these elements reside in theliquid helium bath and thus remain at a constant temperature throughout the measurements, so phaseshifts and changes in coil geometry are minimized.
The Apply Nulling Waveform command in the AC Center Parameters dialog box (see figure 2-6)
disables drive nulling only during AC centering measurements. Quantum Design recommends thatdrive nulling be disabled during AC centering. The extreme precision that nulling allows is unnecessary during centering, and nulling greatly increases the time necessary to complete a centering
measurement.

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CHAPTER

3

AC System Calibration

3.1

Introduction
This chapter contains the following information:•

Section 3 .2 presents an overview of•sys~em calibration.

•

3.2

Section 3.4 describes the process of
performing an absolute calibration.

Section 3 .3 describes the process ofcalibrating the instrument response.

Overview of Calibration
Calibration of an AC susceptometer requires two separate operations. First you identify and remove
the inherent response of the instrument as it varies with the amplitude of the applied field, frequency,
and temperature. Next you perform an absolute calibration of the instrument at a suitable amplitude,frequency, and temperature.

3.3

Instrument Response Calibration
To calibrate the intrinsic response of the MPMS AC system, you measure a sample with a known
dependence on a field, frequency, and temperature. You should ideally use a sample with a precisely
calibrated amplitude and phase response that is a function of both frequency and temperature.
Accurate calibration standards for AC measurements are not available commercially. However, byselecting a material whose imaginary component of the susceptibility X" is zero, you can calibrate
amplitude and phase separately. Dysprosium (III) oxide (Dy20 3) is an electrical insulator with a large
paramagnetic susceptibility. In the frequency range of0.001 to 1000 Hz, its moment is in phase withthe applied field; that is, it is assumed that any component due to resistive or other dissipative mechanisms is too small to measure in the AC system. By knowing thatX" is always zero for Dy20 3 , you
can determine the phase response.

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MPMS AC Option User's Manual

3-1Chapter 3
AC System Calibration

Section 3.3
Instrument Response Calibration

You determine the intrinsic response of an instrument by measuring two components: distortions in
the field applied to the sample and distortions in the measured sample moment. The field you want
to apply to the sample is Ha. The actual field in the sample chamber is the applied internal field Ha,
which has an amplitude change and phase shift relative to Ha. The induced sample moment is Ms.
The measured sample moment Mm has an amplitude and phase shift relative to Ms because of theintervening body of the instrument and the measuring circuit. The determination and removal of
the amplitude and phase shifts in Ha and Mm relative to Ha and Ms are discussed below.
Three concentric tubes made of high-resistivity material thermally isolate the sample from the liquid
helium bath. These tubes are located between the copper solenoid, which produces the AC drive
current, and the sample. The tubes produce frequency and temperature-dependent attenuation andphase shift in the excitation field applied to the sample. In addition, the amplifier circuit producing
the AC drive current contains a 5-kHz, one-pole filter. You can directly determine the frequency
and temperature dependence of the amplitude of the field applied to the sample; you simply use acopper solenoid connected to a spectrum analyzer to measure the field in the sample chamber. The
temperature dependence of Ha is sufficiently small over the range of 2 to 400 K that no correction to
the applied field for changes in the sample temperature is necessary. To account for the frequency
dependence of the amplitude, the experimental data obtained from the test solenoid at 175 K is stored
in a calibration table called genampad. cal. The data is used to supply the necessary compensation
to the amplitude of the applied field Ha and subsequently to Ha.
Determining the absolute phase of the field applied to the sample is unnecessary because the absolutephase has no physical significance. Changes in the phase of Ha due to frequency or temperaturechanges are accounted for during the removal of phase shifts in the measured signal Mm that is causedby the instrument itself.
The most difficult effects to determine are distortions to the measured AC moment caused by the
intrinsic frequency response of the instrument. Fortunately, the frequency response is independentof the amplitude of the AC drive field; this does not imply, however, that the measured amplitude isindependent of frequency. Thus you need only consider calibration of the frequency and temperaturedependence of the amplitude and phase of the measured signal.
Regarding temperature dependence, only the temperature of the inner vacuum sleeve and the sample
chamber tube vary when the sample temperature changes. The SQUID pickup coils and various filters
and amplifiers present elsewhere in the circuit remain unchanged. At very low frequencies, there is
no change in the amplitude and phase shift in the measured signal due to the inner vacuum sleeveand sample chamber tube as a function of temperature. Consequently, any temperature-dependent
effects measured at low frequencies are attributed to the sample and not the system. For example,
the calibration material Dy20 3 is paramagnetic and shows the usual 1IT dependence of its momentat low frequencies, so you normalize all frequency-dependent variations in the measurements to thelow-frequency values at all temperatures.
Before the signal is digitized, it passes through one of five selectable low-pass filters. The MPMS
AC system automatically selects a filter. The wave frequency determines which filter is selected.
Discontinuities in the frequency dependence of the measured signal from these filters are automaticallyremoved by a second-order interpolation procedure that uses a table generated during calibration.
The knowledge that the phase of the susceptibility ofDy20 3 is zero (X" = 0) is sufficient to calibrate
the phase of the sample field as well as the phase shift between Ms and Mm. This is because the phaseshift in the applied field and the intrinsic phase shift of the instrument always appear together and do
not need to be separately determined. By setting the measured phase shift in Mm to zero for Dy20 3,
you remove both individual phase adjustments from the data.

3-2

MPMSAC Option User's Manual

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Section 3.4
Absolute Calibration

Cllllpter 3
AC System Calibration

In addition to varying the AC field amplitude, temperature, and frequency, you can apply DC fields up
to 5 T in either direction along the sample chamber axis. The presence of a DC field produces small
amplitude shifts in the applied AC field via field-induced changes in the screening properties of thesuperconducting magnet wire and the normal conductors present. You correct the amplitude shifts byusing the test coil at different DC fields to measure the internal field. At 5 T, the measured AC fieldvalue is larger than that expected by an amount varying from 2% at 10 Hz to 0.2% at 1 kHz. Thiseffect is accounted for in the software controlling the AC drive coil so that the field applied to thesample is always the field you have specified.

3.4

Absolute Calibration
To perform an absolute calibration of the MPMS AC system, you normalize the measured in-phaseand out-of-phase susceptibilities X' and X" with a sample of known magnetic moment. Absolutecalibration requires a sample known to have negligible frequency dependence in its measured moment,a large susceptibility that is linear in the required range of fields, and no screening currents that canchange its effective shape. Again, Dy20 3 is a suitable sample.
You calibrate the AC measurement by comparing it to a DC measurement. You compare AC and DC
measurements because the AC and DC systems use the identical pickup coils and SQUID detection
system, and the DC system is calibrated from palladium reference standards supplied by the National
Institute of Standards and Technology (NIST). First, you take DC measurements of the Dy203 sample
at several low DC fields. You then repeat the measurement at the same temperature by using a DC
field set by the AC solenoid. The system compares the susceptibilities to measure the BI I (gauss/amp)
ratio of the AC solenoid. The BI I ratio is recorded as Coil Cal 2 in the Low Field calibration group.
Next, you take AC measurements at a low frequency. The system compares the AC and DC
susceptibilities and adjusts the AC regression factor to ensure that the AC and DC susceptibilities
compare as expected. The AC regression factor is an AC calibration factor.
Sine wave generation and analysis are entirely digital, so calibration of the absolute value of ameasured phase is trivial because both the wave period and the interval between data points are
precisely known. The ultimate accuracy with which the phase may be determined is related to thestability of the crystal oscillator controlling all timing signals in the digital circuitry and therefore
places no limitations on the system.
If the inherent sensor noise of the SQUID is the limiting noise source, you can estimate the system
noise level from the noise characteristics of the SQUID detector and the coupling factors between
the SQUID and its detection coils. The SQUID noise referenced to its input is about 6 pA/(Hz) 112(above 0.1 Hz), giving a detector sensitivity for a single SQUID reading of approximately 6 x 10· 12
A· m 2/(Hz) 112, referenced to the corresponding value of magnetic moment. System sensitivity has
been shown to reflect the noise characteristics of the SQUID detector.

Quantum Design

MPMS AC Option User's Manual

3-3

CHAPTER

4AC Sequence Commands
I

4.1

Introduction
This chapter contains the following information:•

4.2

Section 4.2 describes the AC sequencecommands.

Description of AC Sequence Commands
The MPMS AC option includes center, measure, calibration factor, and diagnostic sequencecommands that affect AC operation. The sequence commands automate many of the same tasks,
such as running a measurement, you can perform in immediate mode. AC sequence commands may
be included in a sequence file with any other standard MPMS sequence commands, so you can use
the full functional range of the MPMS MultiVu application while you work with the AC option.
The Magnetic Property Measurement System: MPMS MultiVu Application User's Manual
discusses sequence files and all standard MPMS sequence commands in detail.

4.2.1

AC Center and Measure Sequence Commands

4.2.1.1

AC CENTER

AC Center runs an AC centering measurement. The AC centering measurement uses whateverparameters were last specified with the AC Parameters command. Consequently, in a sequence,
AC Parameters should precede AC Center. AC Center should precede the Adjust Positioncommand.
AC Center is in the Center command group in the sequence command bar.
Section 2.3.4 discusses the AC centering measurement in more detail.

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MPMSAC Option User's Manual

4-1Chapter4

Section 4.2
Description of AC Sequence Commands

4.2.1.2

AC Sequence Commands

AC PARAMETERSAC Parameters defines the AC measurement and SQUID parameters used during the sequencemode AC centering measurement. In a sequence, AC Parameters should precede AC Center.
AC Parameters is in the Center command group in the sequence command bar.
Section 2.3.4.2 discusses in more detail the procedures for setting the centering measurement
parameters.

4.2.1.3

MEASURE AC

Measure AC runs an AC sample measurement and defines the AC measurement and SQUID
parameters used during the sequence-mode measurement.

Measure AC is in the Measure command group in the sequence command bar.
Section 2.3.5 discusses the AC sample measurement and the measurement and SQUID parameters
in more detail.

£!

Measure AC. '''~5mmuJ

ilK

J.

. -

f

. . . . ---- ....... .

< cil~~elFigure 4-1. Measure AC Dialog Box for Sequence Mode

4-2

MPMS AC Option User's Manual

Quantum Design

Section4.2

Chapter4

Description qfAC Sequence Commands

AC Sequence Commands

4.2.1.4

SCAN AC AMPLITUDE

Scan AC Amplitude sets a series of drive amplitudes in a specified amplitude range and thus changes
the drive amplitude for each measurement taken within a control loop. Scan AC Amplitude ignores
whatever drive amplitude the Measure AC or Amplitude command has set.
Scan AC Amplitude is a scan command. Scan commands, unlike other sequence commands, caninstruct the MPMS to perform a task that has multiple parts. The scan command automatically createsa control loop, and the multipart task is performed inside the control loop. A control loop may include
any number of other sequence commands, including other types of scan commands. The Magnetic
Property Measurement System: MPMS MultiVu Application User's Manual discusses scan commands
and control loop operation in detail.

£j- SCAN AC AMPLITUDE -·. -1~a1~mi"Ku¥[UO~~e::. <_fi~IA~crc!_~l5:21893

Oe.,: 0 -~P~~~jNumberof~Steps ::!] -,St~~f2·'·'.J

Figure 4-2. Scan AC Amplitude Dialog Box
PARAMETER

Quantum Design

DEFINITIONVALUES

Initial Amplitude

First set point in amplitude range.

0.0001-5.2189 Oe

Final Amplitude

Last set point in amplitude range.

0.0001-5.2189 Oe

Spacing

Mode of spacing set points.

Number of Steps
Increments (Oe)Log Amplitude

Steps orIncrement

Number of set points.

Steps
Increment

MPMS AC Option User's Manual

4-3Chapter4

Section4.2

AC Sequence Commands

Description ofAC Sequence Commands

4.2.1.5

SCAN AC FREQUENCY

Scan AC Frequency sets a series of drive frequencies in a specified frequency range and thus changes
the drive frequency for each measurement taken within a control loop. Scan AC Frequency ignores
whatever frequency the Measure AC or Wave Frequency command has set.
Scan AC Frequency is a scan command. Scan commands, unlike other sequence commands, caninstruct the MPMS to perform a task that has multiple parts. The scan command automatically createsa control loop, and the multipart task is performed inside the control loop. A control loop may include
any number of other sequence commands, including other types of scan commands. The Magnetic
Property Measurement System: MPMS MultiVu Application User's Manual discusses scan commands
and control loop operation in detail.

£!

- SCAN AC FREQUENCY -!:'~'j~~F~q~~~cJl!~~oo~4s~~~}Hi.2 · •·i','.iHi.;Frequ;~~y~1~12.1~Hz ·~t'~c;~~'!z~~;;~Sl;£;~±1"''-"-'-'·-·i·.·-.. ·.-··__ ,_:_;_·;--;;:·:o_-,:_.· __,_,

i'"T:p· ~~iiJJ ·. ].}~~ l•Figure 4-3. Scan AC Frequency Dialog Box
PARAMETER

4-4

DEFINITIONVALUES

Initial Frequency

First set point in frequency range.

0.00035-1512.1 Hz

Final Frequency

Last set point in frequency range.

0.00035-1512.1 Hz

Spacing

Mode of spacing set points.

Number of Steps
Increments (Hz)Log Amplitude

Steps orIncrement

Number of set points.

Steps
Increment

MPMS AC Option User's Manual

Quantum Design

Section 4.2
Description ofAC Sequence Commands

Chapter4
AC Sequence Commands

4.2.2

AC Calibration Factor Sequence Commands
Calibration factor sequence commands change the AC calibration factors. These commands are in
the Calibration Factors command subgroup, which is in the Diagnostic command group in thesequence command bar.
All AC calibration factor sequence commands have equivalent settings in the Calibration Factors
dialog box. Section 5.2 discusses the AC calibration factors in more detail.
Quantum Design strongly recommends using only the default calibration
factors. Calibration factors may be changed only if a later calibration test has
been performed on the MPMS or if the MPMS must complete nonstandard
tasks. Only personnel who are thoroughly familiar with the MPMS and its
operation should change calibration factors.

CAUTION

4.2.2.1

CURRENT TO FLUXCurrent to Flux sets the ratio of the feedback current to the SQUID signal that is used for calculating
the waveform required to null the AC drive signal.

4.2.2.2

DRIVE RESOLUTION

Drive Resolution sets the ratio of the low-resolution drive range to the high-resolution drive range.
The drive resolution factor ensures that the transition between the low and high drive ranges occurs
smoothly.

4.2.2.3

NULL RESOLUTION

Null Resolution sets the ratio of the low-resolution nulling range to the high-resolution nulling range.
The null resolution factor ensures that the transition Letween the low and high nulling ranges occurs
smoothly.

4.2.2.4

REGRESSION

Regression sets the factor that the system uses to calculate the equivalent EMU value for the AC
response and therefore ensure that AC measurements are consistent with DC measurements. The
range of the regression factor is -5 to +5.
The regression factor is set during absolute calibration of the system.

Quantum Design

MPMS AC Option User's Manual

4-5Chapter4

Section4.2

AC Sequence Commands

Description ofAC Sequence Commands

4.2.3

AC Diagnostic Sequence Commands
All AC diagnostic commands have equivalent settings in the AC Diagnostics dialog box. Section 5.3
discusses the AC diagnostics in more detail.

w

If an AC diagnostic command and an AC measure command define theidentical parameter within a sequence, the system ignores the diagnostic
command and uses the value set by the measure command.

NOTE

4.2.3.l

ACCLOCKFREQUENCYAC Clock Frequency determines the rate at which the system applies the AC drive signal and collects
the resulting data.

4.2.3.2

AC FILTER

AC Filter selects the SQUID filter used for AC processes. The AC Filter command overrides thesystem-selected AC filter. If the wave frequency or clock frequency subsequently changes, the system
continues to use the filter selected with AC Filter.
AC calibration is valid only if the appropriate clock frequency is used with the AC filter. The filter
roll-off frequencies were chosen to give small phase shifts of less than 3 ° at the maximum-intended
drive frequency for each sampling rate. Table 5-2 lists the clock frequency that must be used witheach AC filter.

4.2.3.3

AMPLIFIER GAIN

Amplifier Gain defines the gain of the input amplifier, which is on the AC digitizer card. The gain
value affects system operation only if autoranging is disabled. If autoranging is enabled, the system
automatically adjusts the gain whenever DC offset nulling, line nulling, or an AC measurement isperformed. The input amplifier gain may be x 1, x 10, or x 100.

4.2.3.4

AMPLITUDE

Amplitude defines the amplitude of the AC drive signal the system applies to the sample. The drive
amplitude may be any value from 0.0001 to 5.21893 Oe.

4-6

MPMSAC Option User's Manual

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Section 4.2
Description ofAC Sequence Commands

Chapter4
AC Sequence Commands

4.2.3.5

APPLY NULLING

Apply Nulling, when used in conjunction with the Signal Clocking command, generates a nulling
signal that cancels the effect of the AC drive signal on the SQUID during sample measurements.
Drive nulling must be enabled for the system to accurately measure AC susceptibility. By default,
drive nulling is enabled during sample measurements. If you disable drive nulling, the SQUID sees
the AC drive signal. Apply Nulling does not affect drive nulling during centering measurements.

4.2.3.6

NULL DC OFFSET

Null DC Offset cancels the DC offset. Section 2.5.1 discusses DC offset nulling in detail.

4.2.3.7

NULL LINE NOISE

Null Line Noise cancels the system noise. Section 2.5.2 discusses line nulling in detail.

4.2.3.8

SIGNAL CLOCKING

Signal Clocking sends a drive signal to the Model 1822. The drive signal starts the clock that controls
the output of the signals. If nulling is enabled, Signal Clocking also sends a nulling signal. Signal
Clocking keeps the signals synchronized.

4.2.3.9

STEPS PER CYCLESteps per Cycle determines the number of points the system uses to generate the wave frequency andthe number of data points the system collects during each cycle of data. The number of steps per cycle
must be an integer.

4.2.3.10

TWO-POINT MEASUREMENT

Two-Point Measurement enables two-point AC sample measurements. Two-point measurements,
which are more accurate but slower than one-point measurements, are the system default. A two-point
measurement nulls all field signals except the sample signal and allows an extremely accurate measurement of AC susceptibility. If you disable two-point measurements, the system takes a one-point
measurement at the current position of the sample transport.

4.2.3.11

WAVE FREQUENCY

Wave Frequency defines the frequency of the AC drive signal the system applies to the sample.
The wave frequency may be any value from 0.00035 to 1512.1 Hz.

Quantum Design

MPMS AC Option User's Manual

4-7

CHAPTER

5AC Calibration Factors and Diagnostics

5.1

Introduction
This chapter contains the following information:•

5.2

Section 5.2 discusses the AC calibration
factors.

•

Section 5.3 discusses the AC diagnostics.

AC Calibration Factors
The AC calibration factors ensure the accuracy of AC measurements and set the limits of the AC drive
signal and nulling waveform. The default AC calibration factors are set at the Quantum Design factory
to ensure that the calibration reflects the unique attributes of the AC MPMS system.
All AC calibration factors are listed in the AC group, which is in the Calibration Factors dialog box(see figure 5-1 on the following page). You open the Calibration Factors dialog box by selecting theUtilities>Calibration option. The AC group consists of the current-to-flux ratio, drive resolution
factor, null resolution factor, and regression factor.
Quantum Design strongly recommends using only the default calibration
factors. Calibration factors may be changed only if a later calibration test has
been performed on the MPMS or if the MPMS must complete nonstandard
tasks. Only personnel who are thoroughly familiar with the MPMS and its
operation should change calibration factors.

CAUTION

You select a calibration factor by either double-clicking on it in the AC group or by clicking on it
once and then clicking on the Change button that is near the upper right comer of the Calibration
Factors dialog box. When you select a calibration factor, a pop-up dialog box opens, listing thecurrent value of the calibration factor. If you enter a new value and then select OK, you change
the calibration factor.

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MPMSACOption User's Manual

5-1Chapter 5
AC Calibration Factors and Diagnostics

Section 5.2
AC Calibration Factors

13

Calibration Factms

Magnet (1450. 000)
Longitudinal SQUID (7500.000)
Transverse SQUID (7500.000)
Field Penetration (0.000)
Longitudinal EKtended Range (300. 000)
Transverse EKtended Range (300.000)
Longitudinal Regression Factor (1.825)
Transverse Regression Factor (1.825)
Minimum data points (8)Transverse Rotator steps/degree (96.0000)± SQUID settle time
± Temperature!±1 Low Field

BBCurrent to fluK ratio (·1.000000)

Drive resolution factor (100.00000)
Null resolution factor (1 00. 00000)
Regression factor (0.625000)± RSO

Figure 5-1. AC Group in Calibration Factors Dialog Box

Table 5-1. AC Calibration Factors

CALIBRATION FACTOR

5-2

PARAMETER DEFINEDDEFAULT
VALUE

Current-to-Flux Ratio

Ratio of feedback current to SQUID signal that is used
for calculating waveform required to null AC drive
signal.

-1.000

Drive Resolution Factor

Ratio of low-resolution drive range to high-resolution
drive range. Drive resolution factor ensures that transition between low and high drive ranges is smooth.

100.000

Null Resolution Factor

Ratio of low-resolution nulling range to high-resolution
nulling range. Null resolution factor ensures that transition between low and high nulling ranges is smooth.

100.000

Regression Factor

Factor the system uses to calculate equivalent EMU
value for AC response and therefore ensure that AC
measurements are consistent with DC measurements.
Range ofregression factor is -5 to +5. Regression
factor is set during absolute calibration of the system.

0.625

MPMS AC Option User's Manual

Quantum Design

Section 5.3
AC Diagnostics

Chapter 5
AC Calibration Factors and Diagnostics

5.3

AC Diagnostics
The AC diagnostic settings define several AC measurement parameters and set the rate at which thedrive and nulling signals are sent and data is collected. The two AC diagnostic control commands
immediately null the DC offset or the system noise. All AC diagnostics are in the AC Diagnostics
dialog box (see figure 5-2), which you open by selecting the Utilities> Diagnostics> AC option.
Most diagnostic settings are system specific or are determined by current system settings. You change
the value of a diagnostic setting by either selecting an option or entering a value and then clicking on
the corresponding Set button in the AC Diagnostics dialog box. Any change made to a measurement
parameter also appears in the AC Measurement dialog box.

l!!llil Ei.....

AC Diagnostics[~el\i~.

-]"G:~f:~~~~,~I~oogo_,~2,,, [t]:;L':llf' •..,Qli> :Emo . g ~ ·~1
; ;:;:;.

+ ·.

_;;~~~~~~~~J~s~.627• ·. ...

Set::n;-f~~~~1iy~f~::~~ ~ ··--~·;_ •• -.::.•.
9 000

1 ~5,~@_CIO~irif ' On; n•. Off .•--~· J~P9i;li}vl~~~~i.p": w~~N~~rigo~9ir;
APPtYNulfih9Waveiqn1l:J~ ..

lFigure 5-2. AC Diagnostics Dialog Box

All AC diagnostic settings----except Write Nulling Diag---and controls have equivalent sequencecommands. If you want to change diagnostic parameters automatically, run a sequence that includes
the appropriate diagnostic commands. Section 4.2.2 discusses the AC diagnostic sequence commands.

Quantum Design

MPMSAC Option User's Manual

5-3Section 5.3
AC Diagnostics

5.3.1

Chapter 5
AC Calibration Factors and Diagnostics

AC Diagnostic Settings

5.3.1.1

DRIVE AMPLITUDE

Drive Amplitude defines the amplitude of the AC drive signal the system applies to the sample.
The drive amplitude may be any value from 0.0001 to 5.21893 Oe.

5.3.1.2

AC FILTER

AC Filter selects the SQUID filter used for AC processes. The AC Filter command overrides thesystem-selected AC filter. If the wave frequency or clock frequency subsequently changes, the system
continues to use the filter selected with AC Filter.
AC calibration is valid only ifthe appropriate clock :frequency is used with the AC filter. The filter
roll-off frequencies were chosen to give small phase shifts ofless than 3° at the maximum-intended
drive frequency for each sampling rate. The following table lists the clock :frequency that must be usedwith each AC filter.
Table 5-2. Clock Frequencies Used to Validate AC Calibration
AC FILTER

5.3.1.3

CLOCK FREQUENCY

None

Used only with DC measurements

5Hz

45.776 Hz

lOHz

Used only with DC measurements

80Hz

732.42 Hz

1200Hz11718 Hz

5000Hz

187500 Hz

20,000 Hz

187500 Hz

Elliptical

Used only with DC measurements

GAIN

Gain defines the gain of the input amplifier, which is on the AC digitizer card. The gain value affects
system operation only if autoranging is disabled. If autoranging is enabled, the system automaticallyadjusts the gain whenever DC offset nulling, line nulling, or an AC measurement is performed. The
input amplifier gain may be xl, xlO, or xlOO.

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AC Diagnostics

Chapter 5
AC Calibration Factors and Diagnostics

5.3.1.4

WAVE FREQUENCY

Wave Frequency defines the frequency of the AC drive signal the system applies to the sample.
The wave frequency maybe any value from 0.00035 to 1512.1 Hz.
The wave frequency is a function of the clock frequency and the number of steps per cycle:

ClockFrequency
WaveFrequency = S,p C lteps er ye e
When the wave frequency changes, the system makes whatever adjustments are necessary to the clock
frequency and to the number of steps per cycle. Consequently, when the clock frequency or number ofsteps changes, the system makes whatever adjustments are necessary to the wave frequency. Both theclock frequency and number of steps per cycle must have discrete values: the clock frequency is fixed,
and the number of steps must be an integer. The wave frequency that the system uses may varyslightly from the wave frequency you specify.
When the wave frequency changes and you have not used the AC Filter setting to select an AC filter,
the system selects the optimal AC filter for the new wave frequency.

5.3.1.5

CLOCK FREQUENCY

Clock Frequency determines the rate at which the system applies the AC drive signal and collects theresulting data.
The clock frequency, which is one of five system-defined values, is a function of the wave frequency
and the number of steps per cycle. When the clock frequency changes, the system makes whatever
adjustments are necessary to the wave frequency and to the number of steps per cycle. Consequently,
when the wave frequency or number of steps changes, the system makes whatever adjustments arenecessary to the clock frequency.
Table 5-3. System-Defined Clock Frequencies
CLOCK
FREQUENCYSTEPS PER
CYCLE

WAVE
FREQUENCY

2.861

512-8191

0.0056-0.0003

45.776512-8191

0.0894-0.0056

732.42512-8191

1.4305-0.0894

11719

512-8191

22.888-1.4307

187500124-8190

1512.1-22.894

When the clock frequency changes and you have not used the AC Filter setting to select an AC filter,
the system selects the optimal AC filter for the new clock frequency.

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AC Calibration Factors and Diagnostics

Section 5.3
AC Diagnostics

5.3.1.6

STEPS PER CYCLESteps per Cycle determines the number of points the system uses to generate the wave frequency andthe number of data points the system collects during each cycle of data. The number of steps per cycle
must be an integer.
The number of steps per cycle is a function of the clock frequency and the wave frequency:

StepsPer Cye le =ClockFrequency.
WaveFrequency

When the steps per cycle changes, the system makes whatever adjustments are necessary to the clock
frequency and to the wave frequency. Consequently, when the clock frequency or wave frequencychanges, the system makes whatever adjustments are necessary to the number of steps per cycle.
The number of steps per cycle also defines the memory available to store data points:
2
MaxBlocks = S ,where S is the number of steps per cycle.

5.3.1.7

SIGNAL CLOCKING

Signal Clocking sends a drive signal to the Model 1822. The drive signal starts the clock that controls
the output of the signals. If the Apply Nulling Waveform setting is enabled, Signal Clocking also
sends a nulling signal. Signal Clocking keeps the signals synchronized.
By default, signal clocking is turned on. If you tum off signal clocking, then at the end of the current
wave cycle, the Model 1822 stops the clock controlling the signal output.

5.3.1.8

TWO-POINT MEASUREMENT

Two-Point Measurement enables two-point AC sample measurements. Two-point measurements,
which are more accurate but slower than one-point measurements, are the system default. A two-point
measurement nulls all field signals except the sample signal and allows an extremely accurate measurement of AC susceptibility. If you disable two-point measurements, the system takes a one-point
measurement at the current position of the sample transport.

5.3.1.9

APPLY NULLING WAVEFORM

Apply Nulling Waveform, when used in conjunction with the Signal Clocking command, generates
a nulling signal that cancels the effect of the AC drive signal on the SQUID during sample measurements. Drive nulling must be enabled for the system to accurately measure AC susceptibility. Bydefault, drive nulling is enabled during sample measurements. If you disable drive nulling, the SQUID
sees the AC drive signal. Apply Nulling Waveform does not affect drive nulling during centering
measurements.

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Section 5.3
AC Diagnostics

Chapter 5
AC Calibration Factors and Diagnostics

5.3.1.10

WRITE NULLING DIAG

Write Nulling Diag generates two data files: the drive file and the null file. By default, Write
Nulling Diag is disabled in order to conserve disk space.
The drive, or . drv, file records the angle and voltage of the drive waveform that is used during themeasurement. One block of voltages is written to the . drv file at the end of each measurement.
The null, or . nul, file records waveform characteristics of the nulling drive signal that is generated
during the measurement. A new waveform is generated only when you change the AC parameters.

5.3.2

AC Diagnostic Controls

5.3.2.1

NULL DC OFFSET

Null DC Offset cancels the DC offset. Section 2.5.1 discusses DC offset nulling in detail.

5.3.2.2

NULL LINE NOISE

Null Line Noise cancels the system noise. Section 2.5.2 discusses line nulling in detail.

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5-7

APPENDIXA

Data File Format

A.1

Introduction
This appendix contains the following information:•

A.2

Section A.2 describes and illustrates the
AC data file format.

•

Section A.3 discusses the various
data types.

Format of Data Files
Every data file consists of a header section and a data section. The header defines the type of datastored in the file and the default graph format of the file. The data section lists the actual stored
data. Headers contain the same type of information. Data sections contain data that is specific to
the measurement option that generated the data and to the type of data stored in the file.
The format of the data files is designed such that the files may be easily imported by other graphic
applications, such as Microsoft Excel. The data file format is comma delimited.

A.2.1

Data File Header
The data file header is created when the data file is created, and the data file header can never be
overwritten.
The data file header is preceded by the following bracketed keyword:[Header]

The Title line contains the string that appears at the top of the graph view of the data file.
TITLE, MPMS AC Measurement

The ByApp line specifies which application and measurement option created the file.
BYAPP, MPMS Measurement, 1.0, Summary

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Appendix A
Data File Format

SectionA.2
Format ofData Files

The FileOpenTime line indicates the numerical timestamp and the timestamp's formatted text of thetime at which the file was created.
FILEOPENTIME, 889141960.579000 3/5/1998, 3:52:40 PM
The Info lines supply additional information about the measurement. MPMS MultiVu does not use theinformation in the Info section when it plots the data.
INFO,
INFO,
INFO,
INFO,
INFO,
INFO,
INFO,

NAME, My Sample
WEIGHT, 1.000
AREA, 1.000
LENGTH, 1.000
SHAPE, 0
COMMENT,SEQUENCE FILE: Pause.MV.Seq

The StartupAxes lines indicate which two axes are displayed in the graph view of the data file andwhich data item is assigned to each axis. The StartupAxes lines also indicate whether data is scaled
logarithmically or linearly on the axis, whether the axis is automatically or manually scaled, and theminimum and maximum value for the axis.
STARTUPAXIS, X, 4, LINEAR, AUTO, 0.000000, 0.000000
STARTUPAXIS, Yl, 5, LINEAR, AUTO, 0.000000, 0.000000
The StartupGroup line indicates which field group is the default group for the graph data selection.
STARTUPGROUP, Longitudinal
The FieldGroup lines indicate which data selection items are included in each field group. The
FieldGroup lines list the data items in the numerical urder of their appearance in the file.
FIELDGROUP, Longitudinal, 1, 2, 3, 4, 5, 6, 7, 8 ,9 19
FIELDGROUP, Transverse, 1, 2, 3, 4, 10, 11, 12, 13, 14 19
The PlotAppearance line defines the plot appearance of the graph view of the data file.
PLOT_APPEARANCE, ALL, HORZ_GRID_ON, VERT_GRID_ON, MARKERS
AND LINES

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SectionA.2
Format ofData Files

Appendix A
Data File Format

A.2.2

Data Section
The data section is preceded by the following bracketed keyword:[Data]The data section keyword is immediately followed by one line indicating the titles used for the data
fields for every line of data that follows.

A.2.2.1

DATA SECTION FIELD NAMESAC Measurement Data File: BaseName. ac. dat (one line per measurement)
Time, Comment, Field (Oe), Temperature (K), m' (EMU), m' Std.
Dev., m" (EMU), m" Std. Dev, Amplitude (EMU), Amplitude Std.
Dev., Phase (Deg), Phase Std. Dev., Regression Fit, Drive
Amplitude (Oe), Wave Frequency (Hz), Steps per Cycle, Blocks
to Average, Measurements to Avg., Clock Frequency, Amplifier
Gain, AC Filter, Two Point Measurement, Scan Length, SettlingTime (sec), Delta Temp (K), Rot Position (deg),

AC Diagnostic Data File: BaseName. ac. diag (one line per measurement to average)
Time, Comment, Field (Oe), Average Temperature (K), Target
Temperature (K), m' (EMU), m" (EMU), Amplitude (EMU), Phase(Deg), Regression Fit, Start Temperature (K), Delta
Temperature (K), End Temperature (K), Measurements to Average,
Scan Rejected, High Resolution Mode, Hysteresis, SQUID Range,
SQUID Gain, SQUID Filter, Voltmeter Gain, Digitizer Rate,
Digitizer Readings, Helium Level, Rot Position (deg),

AC Raw Data File: BaseName. ac. raw (one line per data point)Time,Comment,Field (Oe),Start Temperature (K),End Temperature(K),Scan,Rejected,Angle (Deg),First Pt. Voltage,Average First
Voltage,Last Pt. Voltage,Average Last Voltage,Avg. Sample
Response Voltage,First Pt. SQUID Factor,Last Pt. SQUID
Factor,Rot Position (deg),

Nul Data File: BaseName. ac . nul (one line per data point)Time, Comment, Temperature (K), Drive Amplitude, Drive
Frequency (Hz), Offset', Offset", Drive', Drive", Offset
Amplitude, Regression Fit,

Drive Data File: BaseName. ac. drv (one line per data point)Time, Comment, Angle (Deg.)., Voltage (mV), A/D Count,

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Section A.3
Data Types

Appendix A
Data File Format

A.3

Data Types

A.3.1

Numerical Data
Numerical data in a data file may be stored in any standard floating point or integer format with thefields separated by commas. Note, however, that when data is read from the file, any floating point
number that is read into an integer variable is truncated.

A.3.2

Strings
Strings are not delimited by quotation marks, apostrophes, or commas. Furthermore, only one string
should be assigned to each line and no other fields should be on that line. In this format, strings may
then contain any punctuation and can be entered by the appropriate line-entry command in thelanguage of choice.

A.3.3

BooleanBoolean variables should be represented as integers 0 or 1, where 0 indicates FALSE and 1 indicates
TRUE.

A.3.4

Additional Information
This section describes some of the data file fields in more detail.
High Res Mode Enabled (Boolean):0 =Disabled
1 =EnabledThis only returns the software status and does not reflect the fact that above 5000 G
the system charges the magnet with the Low Resolution resistor.
Rotator Position:
If the rotator option is not installed, 0 is always returned.
Hysteresis:
0 = Magnet is persistent
1 = Magnet is not persistent
SQUID Number:
2 = Transverse
1 = Longitudinal

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SectionA.3
Data Types

Appendix A
Data File Format

Range+ (X_Range * 10):
Range is an integer:
O=Xl
1 =XlO
2=Xl003 =XIOOO
X_Range is a Boolean:
O=OFF
l=ON
Values for "Range+ (X_Range * 10)" areExtended range OFF= 0, 1, 2, 3
Extended range ON = 10, 11, 12, 13
Gain (Integer):
0 =XI
1 =X2
2 = X5
3 =XlO
Voltmeter Digitizer Gain:
See Gain
Filter (Integer):
0 = 20,000 Hz (AC orRSO)
1 = 5000 Hz (AC or RSO)
2 = 1200 Hz (AC or RSO)
3 = lOOHz= 80 Hz (AC or RSO)
4 = lOHz
5 = 1 Hz= 5 Hz (AC or RSO)
6 = Elliptical
7 =NoneRate (Integer):
1=60Hz2 = 180Hz
Scan Type (Integer):
1 =Full scan
2 = Linear regression
3 = Iterative regression

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A-5

References

Quantum Design. 1999. Magnetic Property Measurement System: MPMS MultiVu Application User's Manual.
1999. Magnetic Property Measurement System: Reciprocating Sample Option User's Manual.
1990. MPMS Hardware Reference Manual.

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References-1

Index

Absolute calibration, for AC system, 3-3. See also
Instrument response calibration
AC centering measurement
aborting, 2-10
advantages, 2-7
data file, 2-7, 2-10
defining parameters for, 2-8-2-9
plot of, 2-10
procedures,2-7-2-11
AC Center sequence command, 4-1
AC digitizer, description of, 1-3
AC drive system, description of, 1-3
AC filter diagnostic setting, 5-4
AC measurement parameters, list of, 2-12
AC option
calibration factors. See Calibration factors
combining AC drive field with SQUID system, 1-2
diagnostics. See Diagnostics
electronics, overview of, 1-3
measurement. See AC susceptibility measurement
measurement range, 1-2
sample types, 1-2
sequence commands, 4-1-4-7
software, overview of, 1-4
AC Parameters sequence command, 4-2
AC susceptibility measurement
aborting, 2-15
coordinate system options, 2-13
data files, 2-11
description, 2-15, 2-16-2-17
diagnostic settings, 5-3-5-7
overview, 2-1
parameters, list of, 2-12
procedures, 2-2-2-15
attaching sample, 2-2-2-3
centering sample, 2-7-2-11
defining sample parameters, 2-6
inserting sample in sample chamber, 2-3-2-5
measuring sample, 2-11, 2-13-2-15
sample transport options, 2-2
stabilizing system conditions for, 2-11
AC susceptometer, operation of, 1-1
Amplifier gain
for AC centering measurement, 2-9
for AC susceptibility measurement, 2-13
diagnostic setting, 5-4Autoranging, caution against disabling, 2-9, 2-14
Autotracking
caution against disabling, 2-9, 2-14
effect on sample transport initialization, 2-7

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Blocks-to-average parameter
for AC centering measurement, 2-9
for AC susceptibility measurement, 2-14
Calibration, 3-1-3-3
Calibration factors
list of, 5-2
overview, 5-1
sequence commands, 4-5center.ac.lastscan fileplot of, 2-10
saving centering measurement data, 2-7, 2-10
Centering measurement, types of, 2-7. See also
AC centering measurement
Clock frequency diagnostic setting, 5-5Current-to-flux ratio, 5-2
Data files
data types in, A-4-A-5
format, A-1-A-3
selecting for AC susceptibility measurement, 2-14
storing AC centering measurement data, 2-7, 2-10
storing sample measurement data, 2-11
viewing, 2-15
.dat filesaving sample measurement data, 2-11
saving sample parameter data, 2-6, 2-14
selecting, 2-14
DC centering measurement, suggested usage, 2-7
DC offset nullingcommand, 4-7, 5-7
description, 2-17
Diagnostic data file, saving data to, 2-14
Diagnostics
controls, 5-7
overview, 5-3
sequence commands, 4-6-4-7
settings, 5-4-5-7
Drive amplitude
for AC centering measurement, 2-8
for AC susceptibility measurement, 2-13
diagnostic setting, 5-4
Drive file, 5- 7
Drive nulling
description, 2-18
disabling during centering measurement, 2-9, 2-18
importance for AC susceptibility measurement, 2-11
Drive resolution factor, 5-2

MPMSAC Option User's ManualIndex-1

IndexElectronics, for AC system, overview of, 1-3
Instrument response calibration, for AC system, 3-1-3-3.
See also Absolute calibration.lastscan file, 2-11
Line nullingcommand, 4-7, 5-7
description, 2-17-2-18
Measure AC sequence command, 4-2
Measurement. See AC susceptibility measurement
M0asurement data file. See .<lat file
Measurements-to-average parameter
for AC centering measurement, 2-9
for AC susceptibility measurement, 2-14
MPMS MultiVu application, controlling AC system, 1-4
Null amplitude
for AC centering measurement, 2-9
for AC susceptibility measurement, 2-13
Null file, 5-7
Nulling, types of, 2-17
Null resolution factor, 5-2
One-point measurement, enabling, 2-11
Raw data file, saving data to, 2-14
Regression factor, 5-2

Index-2

Sampleattaching to sample rod, 2-2-2-3
centering, 2-7-2-11
inserting in sample chamber, 2-3-2-5
measuring for AC susceptibility, 2-11, 2-13-2-15
parameters, saving to data file, 2-6
types for AC susceptibility measurements, 1-2
Sample transport
initializing, 2-7
options for AC susceptibility measurements, 2-2
Scan AC Amplitude sequence command, 4-3
Scan AC Frequency sequence command, 4-4
Scan data file, 2-11
Settling time
for AC centering measurement, 2-9
for AC susceptibility measurement, 2-14Signal nulling, description of, 2-17-2-18
Software, for AC system, 1-4
SQUID parameters, list of, 2-12
SQUID settling time. See Settling time
Steps-per-cycle diagnostic setting, 5-6
Two-point measurement. See also AC susceptibility
measurement: Description
as default for AC susceptibility measurement, 2-11
enabling, 5-6
procedures for, 2-13-2-15
Wave frequency
for AC centering measurement, 2-8
for AC susceptibility measurement, 2-13
diagnostic setting, 5-5

MPMS AC Option User's Manual

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