National Institute of 

Standards and Technology

Technology Administration

U.S. Department of Commerce

NISTIR 6606

January 2001

Electronics and Electrical 

Engineering Laboratory

Magnetics

Group

Programs, Activities, and 

Accomplishments
The cover illustrates some of the research areas of the EEEL Magnetics Group: magnetic

calibration standards (magnetic-force microscope image of single-domain Co-Pt multilayer

dots, 100 nanometers in diameter, upper right), improvements in data storage density and

data-transfer rate (internal view of a computer hard disk, lower right), new measurement

tools for the magnetic recording industry (inductive current probe for testing write heads,

lower left), and metrology for the superconductor industry (magnetic-resonance image for

medical diagnostics, background).
Electronics and Electrical

Engineering Laboratory

Magnetics

Group

Programs, Activities, and

Accomplishments

NISTIR 6606

January 2001

U.S. DEPARTMENT OF COMMERCE

Norman Y. Mineta, Secretary

Technology Administration

Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Karen H. Brown, Acting Director

ME

UNITED STATES OF AMERICA

DEPARTMENT OF COM

RCE
EEEL Magnetics Group

National Institute of Standards and Technology

325 Broadway

Boulder, Colorado 80305-3328

Telephone: 303-497-5477

Facsimile: 303-497-5316

On the Web: http://www.eeel.nist.gov/magnetics
 Magnetics Group iii

Contents

Welcome .........................................................................................................................iv

Magnetic Recording Measurements.................................................................................... 1

Magnetodynamics ............................................................................................................ 5

Nanoprobe Imaging.........................................................................................................10

Magnetic Thin Films and Devices......................................................................................15

Standards for Superconductor Characterization .................................................................20

Superconductor Electromagnetic Measurements................................................................24

Appendix A: Laboratory Facilities......................................................................................28

Appendix B: Postdoctoral Research Associateships ...........................................................30

Appendix C: EEEL Magnetics Group Staff ..........................................................................34

Appendix D: Prefixes for the International System of Units (SI)..........................................35

Appendix E: Units for Magnetic Properties.........................................................................36
iv Electronics and Electrical Engineering Laboratory

Welcome

The Magnetics Group develops and disseminates unique measurement technology for

industries concerned with magnetic information storage and superconductor power. The

group is located in Boulder, Colorado, part of the Electronics and Electrical Engineering

Laboratory at NIST. It collaborates with the Magnetic Materials Group in Gaithersburg, Maryland, part of the Materials Science and Engineering Laboratory, in developing magnetic calibration standards and in the study of magnetodynamics.

Each of the group’s projects is led by a senior scientist, often assisted by an engineer, technician, postdoctoral research associate, graduate or undergraduate student, or guest research

scientist. The group has six projects:

! Magnetic Recording Measurements

! Magnetodynamics

! Nanoprobe Imaging

! Magnetic Thin Films and Devices

! Standards for Superconductor Characterization

! Superconductor Electromagnetic Measurements

The work of the group spans the range from practical engineering to theoretical modeling.

Some of the projects with unique expertise receive partial support from other government

agencies and industrial consortia.

Research is conducted in areas that include:

! Magnetic calibration standards

! Superconductor standards and best practices

! High-density and high-speed magnetic recording

! Magnetoresistive sensors and memory elements

! Magneto-optic and inductive magnetometry

! Recovery of data from damaged or erased recording media

! Scanned-probe microscopy and micro-electromechanical systems

! Electromechanical properties of superconductors

The group disseminates the results of its research through publications in refereed journals,

presentations at conferences and workshops, and participation in standards organizations.

For additional information about the EEEL Magnetics Group, please visit our Web site at

http://www.eeel.nist.gov/magnetics. Thanks for your interest in the EEEL Magnetics Group.

— Ron Goldfarb, Acting Group Leader
 Magnetics Group 1

Magnetic Recording Measurements

Project Goals

This project addresses national measurement

needs in magnetic data storage for industry,

advanced applications, and national security. It is

developing novel calibration standards, ranging

from active inductive standards for magnetometers to standards for the determination of the

absolute magnetic moment of thin magnetic

films. Using state-of-the-art vacuum technology

and spin-resolved electron spectroscopy, project

members are doing research on the magnetic

anisotropy of thin films used in data storage.

Magnetic imaging techniques and measurements

are developed for the authentication of recorded

information and the recovery of data from samples of damaged magnetic recording media. The

project has recently developed new techniques

for imaging forensic evidence for the Federal

Bureau of Investigation (FBI) and for data recovery for the National Transportation Safety Board

(NTSB). It has published definitive work on

magnetic reorientation transition of ultra-thin

(two atomic layers) films of iron on gadolinium

as well the magnetic phase transition of the

atomically clean gadolinium surface.

David Pappas and Steve Arnold in the Magnetic

Recording Measurements lab.

Customer Needs

Magnetic data storage has been a growing industry this entire century. With the advent of widespread use of computers and mass-storage media,

it can be expected to continue to grow for the

foreseeable future. Magnetic data storage products include analog audio and video products in

various formats (standard and micro-cassettes,

audio tapes, VHS), digital-media removable data

storage (digital audio tapes, floppy disks,

read/write compact disks), and non-removable

data storage such as hard disk drives and airline

flight data recorders. Because of this wide range

of products, there are many customers for magnetic-recording metrology. The hard-disk-drive

industry represents the cutting edge of technology in this area, highly competitive in terms of

both scientific development and profit margins.

The requirements of the high-density storage

industry for reproducible fabrication of thin

magnetic films has pushed quality assurance to

its limit. This extends to a wide range of magnetic properties and requires magnetometers that

are calibrated over many orders of magnitude in

sensitivity. We are currently working on a number of novel methods to standardize magnetic

moments of thin films.

Forensic analysts are constantly battling to keep

up with the combined effects of increased usage

of magnetic recording and the improved technology that allows higher densities. We address

these needs by utilizing state-of-the-art magnetoresistive sensors to study relatively low-density

storage media (analog audio, VHS) most encountered by the forensics investigator. In addition, the possibility of recovering digital data

from recording media that were either intentionally erased or accidentally damaged is an important problem in criminal and airline-crash investigations.

Technical Strategy

A three-pronged approach is utilized. This includes standards development, imaging with

advanced magnetoresistive heads for forensic

analysis, and in-situ surface magnetometry for

metrology and scientific research. In order to

respond to immediate needs of the data-storage

industry and the magnetic instrumentation companies that service it, three types of magnetometer reference samples are being developed in

collaboration with instrument manufacturers.

These will be magnetic thin-film coupons that

have an integral superconducting fluxmeasurement loop, an inductive magnetic-flux

standard, and a zero-coercivity standard.

MILESTONE: In 2001, fabricate planarized

magnetic/superconducting samples.

MILESTONE: By 2002, measure and standardize flux 

in integrated magnetic/superconducting samples.

Project Leader:

David Pappas

Staff-Years (FY 2000):

1 professional

1 contractor

1 student

Funding Sources:

NIST (70%)

Other (30%)

Parent Program:

Magnetics
 2 Electronics and Electrical Engineering Laboratory

Three-dimensional perspective view of magnetic

bits on recording tape. A section of the tape was

erased and then “NIST” was written.

In 1996 NIST initiated a five-year program to

develop competence in the area of metrology for

magnetic data storage. This program has resulted

in advanced measurement techniques for imaging

information stored on magnetic media with high

resolution and relative ease. The Nanoscale

Recording System (NRS) developed under this

program is a general-purpose instrument that uses

read-write heads similar to those in computer

hard disk or tape drives to image and write data

on magnetic media. The NRS can image by

rastering either the head with computer controlled micrometers with 50 nanometer resolution

or the storage medium with a piezoelectric x-y

stage with 1 nanometer resolution. The NRS is

being used as a prototype for forensic analysis of

audio tapes.

MILESTONE: In 2001, develop high-speed, highresolution metrology for magnetic recording tape.

Magnetic fields above a sample of recording tape.

A test tone was recorded from the left and right

channels of a stereophonic system (rear, right).

On the same tape, a stop mark from the write

head of a monaural telephone-answering machine is imaged (front, left).

It has been shown that high-speed imaging of

samples can be accomplished, and the signatures

of erase heads and write heads have been identified on test samples. In addition, reconstruction

of both analog and digital data from test samples

has been accomplished.

The NRS is capable of detecting magnetic fields

due to currents. This is useful for failure analysis

of very-large-scale-integration (VLSI) chips,

where it is necessary to locate the source of a

current drain due to a short circuit somewhere in

a buried circuit. By imaging the fields and inverting Maxwell’s equations within the appropriate limits, an important metrological tool is being

developed for the semiconductor industry.

MILESTONE: In 2001, measure field distributions of

current leakage in VLSI chips.

Three-dimensional plot of the magnetic fields

100 micrometers above a photolithographed

meander line carrying 10 milliamperes of current.

Basic research is being conducted in the area of

surface and interfacial magnetism. This area is

important for development of metrology relevant

to advanced devices, such as giant magnetoresistive heads, tunnel junctions, and perpendicular

recording media. In our surface science laboratory, we use spin-resolved electron spectroscopy

as a magnetometer to characterize band structure.

MILESTONE: By 2002, measure spin-polarized 

electron excitations in magnetic quantum wells, both

metallic and semiconducting.

All three components of spin polarization are

analyzed, allowing us to study any type of recording media. The electrons are sensitive to the

first few atomic layers of the surface.

MILESTONE: By 2002, measure surface magnetism 

of magnetic semiconductors.
 Magnetics Group 3

Accomplishments

! New Technique for Recovering Data — In

collaboration with the National Telecommunications and Information Administration’s Institute

for Telecommunication Sciences, we developed a

new technique for recovering audio and digital

data from mangled tapes or other storage media

that allows for much more complete and accurate

analysis. Termed “second-harmonic magnetoresistive microscopy” (SH-MRM), this technique

makes use of high-resolution magnetic sensors

developed for modern computer hard-disk drives.

These sensors are used to map the microscopic

magnetic fields across samples, thereby allowing

investigators to reconstruct the original signal

and gain insight into the recording process and

history. To forensics analysts, this can provide

critical information regarding the authenticity of

evidence. We have imaged a number of samples

from other government laboratories. A demonstration of this technique was the recovery of

audio data from a tape fragment provided by the

NTSB laboratory. We showed that raw digital

data can be read from a very short segment of

tape from a flight data recorder. Small bits of

tape are occasionally all that can be recovered

from a major accident. While such segments may

hold the key to the investigation, they are unreadable in a conventional tape deck. Images from

sample audio cassette recordings provided by the

FBI’s Engineering Research Facility Audio

Laboratory revealed magnetic marks produced by

the erase and record heads during the recording

process. In the hands of experts, these data may

allow for authenticity verification. It was shown

that the audio data from test tracks can be reconstructed and played back directly from the SHMRM images. This information is independent of

the normal inductive read process, and can be

critical in the evaluation of recorded evidence

produced for federal criminal-law cases.

! IDEMA Task Force — In collaboration with

the International Disk Drive Equipment and

Materials Association (IDEMA), we participated

in a task force to (a) write a standard method for

measuring magnetic properties and (b) design a

new interlaboratory comparison to test the written standard. The study will include industry and

instrument manufacturers and is targeted at

understanding the needs of the industry and how

NIST and the instrument manufacturers can

accommodate them.

! Magnetic Thin-Film Standards — We manufactured wafers comprised of thin-film magnetic

coupons with integrated superconducting flux

measurement loops. These samples will be tested

for use as thin-film magnetic Standard Reference

Materials. The effects of planarization of the

spacer layers between the magnetic and superconducting films is ongoing.

! Solenoid Flux Standards — A process was

developed for fabricating thin-film solenoid flux

standards. This involved fabricating two layers of

Cu wires separated by an insulating polyimide

layer, with via conductors between the two layers. Special lithographic features were incorporated for accurate determination of the solenoid

dimensions, such as the thicknesses of the Cu and

polyimide layers. The first flux prototypes have

been completed, and tests are underway.

! Models for Flux Standards — Mathematical

models were conducted for the active magnetometer calibration sample that showed that field

accuracy of better than 1 percent is feasible in a 1

nanoweber standard. The models showed that,

within 1 percent, the flux was relatively insensitive to typical errors in solenoid positioning in

the magnetometer. It was found that Dy2O3-

based paramagnetic samples would satisfy the

requirements of a zero-coercivity standard. The

key material properties are high paramagnetic

permeability, high chemical purity, and low

electrical conductivity. The target flux for the

present standard is 10 milliwebers per tesla while

producing less than 1 picoweber in remanence

due to eddy-current artifacts in a field of 0.02

tesla. Tests on the first prototype zero-coercivity

reference sample are underway.

! Surface Studies of Ultrathin Fe Layers on

Thin Gd(0001) — We showed that this system

has a two-step reorientation transition as the

temperature is increased. At low temperatures,

the Fe remains in-plane, antiferromagnetically

coupled to the Gd. At the intermediate temperature, the Fe/Gd surface undergoes a continuous

rotation to a canted direction. Because the exchange coupling in Gd is small, domain walls are

narrow, and we expect an inhomogeneous magnetization depth profile in the Gd thin films in

this intermediate temperature range. Available

models in ultrathin films assume a homogeneous

magnetization and exclude the coexistence of

continuous and discontinuous behavior within

one 90 degree reorientation. The inclusion of a

magnetization depth profile is probably necessary

to reveal the underlying physics in this system.

! Surface Magnetization of Rare Earths Measured — It has long been believed that some rare-
 4 Electronics and Electrical Engineering Laboratory

earth metals (e.g., Gd and Tb) have a surface that

is so much more magnetic than the bulk that the

critical temperature, where long-range order

vanishes, is higher than that in the bulk. Some

studies indicated possible enhancements of 30 to

80 degrees. We have concluded an extensive

study of the Gd surface and find that there is no

enhanced surface critical temperature. The study

required temperature measurement, the analysis

of spins of electrons emitted from the surface,

and the measurement of light ellipticity from the

sample with unprecedented accuracy. This startling result illustrates some of the pitfalls and

shortcomings of existing techniques, including

interpretations of electron spectroscopy data.

Recent Publications

D. P. Pappas, C. S. Arnold, G. Shalev, C. Eunice, D. Stevenson, S. Voran, M. E. Read, E. M. Gornley, J. Cash, K. Marr,

and J. J. Ryan, “Second Harmonic Magneto-Resistive Imaging to Authenticate and Recover Data from Magnetic Storage

Media,” Conf. on Law Enforcement Technology, Proc. SPIE,

in press.

C. S. Arnold and D. P. Pappas, “Gd(0001): A Semi-Infinite

Three-Dimensional Heisenberg Ferromagnet with Ordinary

Surface Transition,” Phys. Rev. Lett., 85, 5202-5205 (December 2000).

C .S. Arnold, D. P. Pappas, and A. P. Popov, “Second and

First Order Phase Transitions in the Magnetic Reorientation

of Fe/Gd,” Phys. Rev. Lett., 83, 3305-3308 (October 1999).

C. S. Arnold, D. P. Pappas, and A. P. Popov, “Magneto-Optic

Kerr Effect Study of a Two-Step Reorientation Transition of

an Ultrathin Magnetic Film,” J. Appl. Phys., 87, 5478-5480

(May 2000).

T. Komesu, C. Waldfried, J. Hae-Kyung, D. Pappas, T.

Rammer, M. E. Johnston, T. J. Gay, and P. A. Dowben,

“Apparatus for Spin-Polarized Inverse Photoemission and

Spin Scattering,” Proc. SPIE 3945, 6-16 (2000).

D. P. Pappas, C. S. Arnold, and A. P. Popov, “Spin Reorientation Phase Transition of Ultrathin Fe Films Grown on

Gd(0001),” in Magnetism and Electronic Correlations in

Local-Moment Systems: Rare Earth Elements and Compounds, M. Donath, P. A. Dowben, and W. Nolting, eds.,

World Scientific, 141-152 (1999).

C. S. Arnold, M. Dunlavy, D. Venus, and D. P. Pappas,

“Magnetic Susceptibility Analysis of the Relaxation-Time for

Domain-Wall Motion in Perpendicularly Magnetized, Ultrathin 1.5 ML Fe/2 ML Ni/W(110) Films,” J. Magn. Magn.

Mater. 198-199, 465-467 (June 1999).

C. S. Arnold, D. P. Pappas, and D. Venus, “Domain Formation Near the Reorientation Transition in Perpendicularly

Magnetized Ultrathin Fe/Ni Bilayer Films,” J. Appl. Phys. 85,

5054-5059 (April 1999).
 Magnetics Group 5

Magnetodynamics

Project Goals

This project develops instruments, techniques,

and theory for the understanding of the highspeed response of commercially important magnetic materials. Techniques used include linear

and nonlinear magneto-optics and inductive

response. Emphasis is on broadband (above 1

gigahertz), time-resolved measurements for the

study of magnetization dynamics under largefield excitation. Research concentrates on the

nature of coherence and damping in ferromagnetic systems and on the fundamental limits of

magnetic data storage. Exploratory research on

spintronic systems and physics is underway. The

project provides results of interest to the magnetic-disk-drive industry, developers of magnetic

random-access memories (MRAM), and the

growing spintronics community. Recent results

include the observation of deleterious magnetic

turbulence during the magnetic switching process, evanescent flux-pulse propagation in metallic

films, and anisotropic coupling (“damping”)

between uniform excitations and the crystal

lattice. Coherent-control methods have been used

to switch magnetization without unwanted precessional ringing. Recently, an inductive current

probe was developed to assess trace-suspension

interconnects for disk-drive recording heads.

Inductive current probe in microwave test station.

Customer Needs

Our primary customers are the magnetoelectronics industries. These include the magnetic-disk-drive industry, the magnetic-sensor

industry, and those companies currently developing MRAM. As commercial disk drives approach data-transfer rates of 1 gigabits per second, there is increased need for an understanding

of magnetization dynamics. In addition, measurement techniques are needed that can quantify

the switching speeds of commercial materials.

Once the response of a material has been benchmarked, the engineer can then develop electronic

components (e.g., heads, disks, or MRAM) that

can fully exploit the bandwidth potential of the

material. We are also providing novel metrology

for the burgeoning spintronics industry. The spin

precession of charge carriers in semiconductor

hosts has significant potential for telecommunications applications. Unlike the case of conventional semiconductor switching, the frequency of

spin precession is not fundamentally limited by

the physical thickness of dielectric spacers. We

plan to investigate novel magnetic/semiconductor

heterostructures of interest to the telecommunications industry.

Technical Strategy

The focus of this project is the measurement of

switching time of magnetic materials for applications in data storage. This has led to the development of cutting-edge instrumentation and

experiments using magneto-optics and microwave circuits. Microwave coplanar waveguides

are used to deliver magnetic-field pulses to

materials under test. In response, the specimen’s

magnetization switches — but not smoothly.

Rather, the magnetization vector undergoes

precession, much as a spinning top precesses in

the Earth’s gravitational field. Sometimes, the

magnetization can precess nonuniformly, resulting in the generation of spin waves or, in the case

of small devices, incoherent rotation.

MILESTONE: During 2001-2003, improve understanding of ferromagnetic switching processes.

Our technical strategy is to identify future needs

in the data-storage and other important industries,

develop new metrology tools, and do the experiments and modeling to provide data and theoretical underpinnings.

We concentrate on two major problems in the

magnetic-data-storage industry: (1) data-transfer

rate, the problem of gyromagnetic effects, and the

need for large damping without resorting to high

fields; and (2) storage density and the problem of

thermally activated reversal of magnetization.

Data-transfer rates are increasing at 40 percent

per year (30 percent from improved linear bit

Project Leader:

Tom Silva

Staff-Years (FY 2000):

2 professionals

1 postdoctoral associate

1 guest researcher

Funding Sources:

NIST (80%)

Other (20%)

Parent Program:

Magnetics
6 Electronics and Electrical Engineering Laboratory

density and 10 percent from greater disk rotational speed). The maximum data-transfer rate is

currently 50 megabytes per second. In five years,

frequencies for writing and reading will be in the

microwave region, which raises the question,

“How fast can magnetic materials switch?”

MILESTONE: By 2002, continue development of 

noninvasive inductive current probe for measurement

of current rise-times in trace-suspension

interconnects between disk-drive heads and

write-current drivers.

MILESTONE: During 2001-2003, develop methods 

for the quantitative study of high-speed switching 

in ferromagnetic films.

The current laboratory demonstration record for

storage density is 9 gigabits per square centimeter

(60 gigabits per square inch). How much farther

can longitudinal media (with in-plane magnetization) be pushed? Can perpendicular recording or

discrete data bits extend magnetic recording

beyond the superparamagnetic limit at which

magnetization becomes thermally unstable? As

the data-storage industry seeks its own answers to

these pressing questions, we must strive to provide the necessary metrology to benchmark the

temporal performance of new methods of magnetic data storage.

We have sought to extend magneto-optics for the

quantitative measurement of magnetization

dynamics in practical ferromagnetic films. Methods include time-resolved generalized magnetooptic ellipsometry (TRe-GME), time-resolved

second-harmonic magneto-optic Kerr effect

(TRe-SHMOKE), and quantitative wide-field

Kerr microscopy (our “MOKEroscope”). All

these systems rely upon rf waveguide technology

for the delivery of fast magnetic field pulses to

excite magnetization switching in specimens. We

use several methods to detect the state of magnetization as a function of time. These include the

following:

! The magneto-optic Kerr effect (MOKE)

makes use of the rotation of polarization of light

upon reflection from a magnetized film. We have

used MOKE with an optical microscope to measure equilibrium and nonequilibrium decay of

magnetization in recording media.

! The second-harmonic magneto-optic Kerr

effect (SHMOKE) is especially sensitive to

surface and interface magnetization. We have

used SHMOKE for time-resolved, vectorial

measurements of magnetization dynamics and to

demonstrate the coherent control of magnetization precession.

Your experiments on

very fast switching in

magnetic films are

well designed and

incisive. They are

exactly the right kind

of experiments that

should be done at an

institution like NIST.

It advances the

science of metrology,

and requires facilities,

both human and

economic, which will

coexist in no other

kind of institution.

Prof. Robert L. White

Director

Center for Research on Information Storage Materials

Stanford University

Simplified schematic of the TRe-SHMOKE system. This system can be used to evaluate the switching

response of thin films to 7 gigahertz excitations.
 Magnetics Group 7

TRe-SHMOKE system for the measurement of

magnetization dynamics with time resolution of

20 picoseconds.

! In our pulsed inductive microwave magnetometer (PIMM), the changing magnetic state of

a specimen is deduced from the change in inductance of a waveguide. This technique is fast,

inexpensive, and easily transferable to industry. It

may also be used as a time-domain permeameter

to characterize magnetic materials.

Pulsed inductive magnetometer for measuring

the switching dynamics of thin magnetic films.

MILESTONE: Upgrade the PIMM to a selfcontained user facility for use by industrial

collaborators to measure switching speeds of

standard and proprietary materials.

While the aforementioned instruments have

immediate use for the characterization of magnetic data-storage materials, they are also powerful tools for the elucidation of magnetodynamic

theory. The primary mathematical tools for the

analysis of magnetic switching data are essentially phenomenological. As such, they have

limited utility in aiding industry in its goal to

control the high-speed switching properties of

heads and media. We have sought to provide firm

theoretical foundations for the analysis of timeresolved data, with special emphasis on those

theories that provide clear and unambiguous

predictions that can be tested with our instruments.

We are committed to supporting new magnetic

technologies as they emerge in the 21st century.

Spintronics is a novel direction in electronics that

promises to revolutionize telecommunications

and information processing. The essential idea

behind spintronics is the manipulation and control of the quantum-mechanical spin of a semiconductor charge carrier. The extension of electronic manipulation toward the spin degree-offreedom has intrinsic advantages that warrant

further exploration. For example, the fundamental problem with high-frequency semiconducting

devices is nonzero resistance R coupled with gate

capacitance C. In essence, the RC time constant

limits the maximum frequency attainable. A key

feature of spin-based rf circuitry is the fundamentally quantum-mechanical nature of spin

precession. Spin precession frequencies are not

intrinsically limited by loss mechanisms such as

carrier mobility, as long as coherence can be

preserved. Spintronics technology holds the

promise of extending telecommunications frequencies into the terahertz regime.

MILESTONE: By 2002, measure precessional dynamics

in spintronic components using time-resolved

magneto-optics.

MILESTONE: By 2003, investigate practical 

applications of spin-momentum transfer effect in

magnetic heterostructures.

Accomplishments

! New Field Sources — We built two computer-controlled field sources that allowed our

inductive current-probe measurements to be

automated and improved the accuracy and consistency of our measurements. We have made

dozens of measurements in a tenth of the time

previously required. A bandwidth of 6 gigahertz

has been achieved in the deconvolved results for

the step-current rise time when using a supplemental bias field to improve the Ni-Fe response.

! New Theory for Damping in Ferromagnetic

Resonance — We have developed a theoretical

framework for understanding damping in ferromagnets. We analyzed the damping mechanism

in the case of direct coupling between the electron spins and the crystal lattice within the context of the quantum-mechanical magnetodynamic

I am very impressed

by the results that

Tom Silva obtained

with the high speed

current probe that he

designed, fabricated

and tested. I was

skeptical that any

ferromagnetic

material could be

used in this context,

but he did it and it

works. This will be a

valuable tool for

diagnosing the write

current in high-speed

drive applications.

Dr. Mike Mallary

Quantum Fellow

Quantum Corporation
8 Electronics and Electrical Engineering Laboratory

equation originally proposed by Herbert Callen in

1958. Callen’s landmark work analyzed the

process of ferromagnetic relaxation as the sum of

three distinct processes: direct coupling between

the uniform precession and the lattice, dissipation

via spin wave generation, and coupling of spin

waves to the crystal lattice. We found that one

can calculate the direct coupling term in the

relaxation equation using conservation of angular

momentum and a quantum-mechanical description of the fundamental spin relaxation process.

An implication of the calculation is that the direct

relaxation process is a function of the magnetization angle relative to the crystalline anisotropy

axis. For magnetization oriented along the easy

axis, direct relaxation is a maximum. For orientation along the hard axis, direct relaxation is

forbidden by simple symmetry considerations.

Thus, relaxation (damping) is dominated by spinwave generation when the magnetization is

orthogonal to the anisotropy axis.

Vector evolution of magnetization after application of field pulse along +x direction. The spirallike path is the result of precessional dynamics

for ferromagnetic spins.

! Damping Theory Applied to Magneto-Optic

Data — We used our new theoretical description

of damping to interpret our recent SHMOKE data

where we found that the magnitude of the magnetization can be strongly reduced immediately

after application of a strong field pulse. The

reduction occurred only if the magnetization was

initially oriented along the hard axis prior to

application of the pulse. We determined that the

Callen model can be used to fit the time dependence of the magnetization reduction with a single

fitting parameter: the quantum-mechanical rate of

spin-wave generation. We found that the rate of

spin-wave generation greatly increases for large

pulses in excess of 560 amperes per meter. This

has profound implications for the disk drive

industry, where very large field pulses are routinely used in the operation of a recording head.

Time-evolution of magnetization after application of field pulse. Material is 50 nanometer thick

Ni-Fe, a common magnetic alloy in disk-drive

recording heads. The measured switching time of

500 picoseconds implies an intrinsic bandwidth

of 700 megahertz. The solid curve is a fit to the

data based on the Landau-Lifshitz-Gilbert equation.

! Spins at a Surface: Are They Faster? — We

are comparing surface and bulk magnetodynamics in thin films of Ni-Fe. Using second-harmonic

and conventional forms of the magneto-optic

Kerr effect (SHMOKE and MOKE) and measuring the response to a field pulse, we found that

the surface and bulk dynamics are almost indistinguishable from each other. The ability to

measure both effects simultaneously using the

same pulsed laser source removes many possible

sources of systematic error. Our error analysis

will set quantitative bounds on the similarity of

surface and bulk magnetodynamics. This study

should be of great interest to those modeling

dynamics in recording-head materials, where

there is general disagreement as to the role of

eddy currents.

! Assessing the Performance of Chaff at RF —

We extended our work on measurements of the

resistance of carbon fibers to high frequencies.

We are using two approaches: The first is a direct

measurement of resistance calibrated against

known resistors specified for 20 gigahertz operation. The second is a method using Fourier analysis of time-domain reflectometry measurements

to extract resistance versus frequency. This

method is simpler experimentally but requires

more difficult analysis.

! Amplifying the Electron Spin: A Proposed

Spintronics Device — In collaboration with the

Magnetic Thin Films and Devices Project, CorI have been especially

impressed by the

novel optical

techniques for

accurate time

resolution of ultrafast

spin dynamics. They

provide, for the first

time, clear

experimental

evidence for

appreciable deviation

from magnetization

magnitude

conservation for

ultrafast magnetic

switchings.

Prof. Isaak Mayergoyz

University of Maryland
 Magnetics Group 9

nell University, and Motorola Corporation, we

developed a novel spintronics device concept: the

spin amplifier. It is based on the recent experimental results at Cornell, where a resonant enhancement of the giant magnetoresistance was

observed in nanoscale devices in the presence of

large magnetic fields. According to the theory,

the spins that constitute a ferromagnet enter a

massively degenerate excited state at the bottom

of the spin-wave spectrum under conditions of

sufficiently large dc current, reminiscent of the

stimulated emission process that drives a laser.

We plan to use such a device for the injection and

detection of coherently precessing spins in a

semiconductor host. As a spin injector, a

“SWASER” (spin-wave amplification by stimulated emission of radiation) is unique in that it

prepares spins in a coherent superposition of “up”

and “down” states (parallel and antiparallel to an

applied magnetic field) before injection into a

semiconductor. Such a coherent superposition

has intrinsic, statistical advantages compared to a

polarized spin current.

! Advanced High-Moment Head Material

Benchmarked — In collaboration with the Materials Science and Engineering Department at

Stanford University, we measured the switching

speed of Fe-Co-N films with the PIMM system.

Our collaborators at Stanford discovered that

they can greatly improve the uniaxial orientation

of sputtered, high-moment, iron nitride films

through use of Permalloy (Ni0.8Fe0.2) as a seed

layer. We found that the materials exhibit an

intrinsic switching speed of 200 picoseconds,

more than a factor of two faster than conventional head materials. The highest-quality films

were surprisingly well damped in their precessional response. Such desirable response is coincident with the observation of an anomalous

second-harmonic component in the time-resolved

data that may contribute to the large damping.

The physics of this effect are still under investigation.

! Flux Propagation Speed Measured in Recording Head Material — The spatial propagation of magnetic flux pulses launched in thin-film

Ni-Fe were measured using TRe-SHMOKE. The

energy propagation velocity, or “group velocity,”

was found to be 105

 meters per second in a film

that was 400 nanometers thick. Such a fast speed

is consistent with the predictions of Damon and

Eshbach’s magnetostatic spin-wave theory. It

was also found that the decay of the flux pulse

was consistent with a damping parameter of 0.02.

Such a value for damping is typical for Ni-Fe

films. These results suggest that the usual quasistatic calculations for the recording efficiency of

disk-drive heads may be erroneous in the limit of

precessional dynamics.

Recent Publications

T. J. Silva and P. Kabos, “Non-Linear Magneto-Optical

Observation of Transient Spin-Wave Excitation in a Ferromagnetic Film Undergoing Large-Angle Switching,” IEEE

Trans. Magn., in press.

P. Kabos, S. Kaka, S. E. Russek, and T. J. Silva, “Metastable

States in Large Angle Magnetization Rotations,” IEEE Trans.

Magn., in press.

A. Moser, D. Weller, N. D. Rizzo, and T. J. Silva, “Determination of Average Demagnetizing Fields in Longitudinal

Magnetic Recording with Nanosecond Pulses,” Appl. Phys.

Lett. 77, 1505-1507 (September 2000).

C. Alexander, Jr., J. Rantschler, T. J. Silva, and P. Kabos,

“Frequency- and Time-Resolved Measurements of FeTaN

Films with Longitudinal Bias Fields,” J. Appl. Phys. 87,

6633-6635 (May 2000).

M. Löhndorf, J. Moreland, P. Kabos, and N. D. Rizzo,

“Microcantilever Torque Magnetometry of Thin Magnetic

Films,” J. Appl. Phys. 87, 5995-5997 (May 2000).

P. Kabos, A. B. Kos, and T. J. Silva, “Vectorial SecondHarmonic Magneto-Optic Kerr Effect Measurements,” J.

Appl. Phys. 87, 5980-5982 (May 2000).

T. M. Crawford, P. Kabos, and T. J. Silva, “Coherent Control

of Precessional Dynamics in Thin Film Permalloy,” Appl.

Phys. Lett. 76, 2113-2115 (April 2000).

N. D. Rizzo, T. J. Silva, and A. B. Kos, “Nanosecond Magnetization Reversal in High Coercivity Thin Films,” IEEE

Trans. Magn. 36, 159-165 (January 2000).

N. D. Rizzo, T. J. Silva, and A. B. Kos, “Relaxation Times for

Magnetization Reversal in a High Coercivity Magnetic Thin

Film,” Phys. Rev. Lett., 83, 4876-4879 (December 1999).

Z. Celinski, D. Lucic, N. Cramer, R. E. Camley, R. B.

Goldfarb, and R. B. Skrzypek, “Exchange Biasing in Ferromagnet/Antiferromagnet Fe/KMnF3,” J. Magn. Magn. Mater.

202, 480-484 (August 1999).

T. J. Silva, C. S. Lee, T. M. Crawford, and C. T. Rogers,

“Inductive Measurement of Ultrafast Magnetization Dynamics in Thin-Film Permalloy,” J. Appl. Phys. 85, 7849-7862

(June 1999).

T. M. Crawford, T. J. Silva, C. W. Teplin, and C. T. Rogers,

“Subnanosecond Magnetization Dynamics Measured by the

Second-Harmonic Magneto-Optic Kerr Effect,” App. Phys.

Lett. 74, 3386-3388 (May 1999).

S. E. Russek, T. M. Crawford, and T. J. Silva, “Study of

NiFe/Al/Al2O3 Magnetic Tunnel Junction Interfaces Using

Second-Harmonic Magneto-Optic Kerr Effect,” J. Appl. Phys.

85, 5273-5275 (April 1999).

G. M. Sandler, H. N. Bertram, T. J. Silva, and T. M. Crawford, “Determination of the Magnetic Damping Constant in

NiFe Films,” J. Appl. Phys. 85, 5080-5082 (April 1999).

T. J. Silva and T. M. Crawford, “Methods for Determination

of Response Times of Magnetic Head Materials,” IEEE

Trans. Magn. 35, 671-676 (March 1999). 

We need the NIST

sub-nanosecond

switching,

experimental, realmaterials viewpoint.

Dr. Gordon Hughes

Associate Director

Center for Magnetic Recording

Research

University of California at San

Diego
 10 Electronics and Electrical Engineering Laboratory

Nanoprobe Imaging

Project Goals

This project develops scanned-probe microscopy

(SPM) and micro-electromechanical systems

(MEMS) for nanometer-scale magnetic measurements in support of the magnetic data storage

industry. Project members perform research to

understand and relate SPM images and MEMS

magnetometer measurements to the performance

of magnetic materials and devices for future

recording technologies. The project is currently

focusing on ultra-small magnetic-force microscopy tips for imaging recording heads and media

at a resolution of 20 nanometers. Quantitative

field mapping of heads and media is based on

electromechanical detection of magnetic resonance. MEMS magnetometers with integrated

specimens and high sensitivity are being developed. Over the next few years, the project will

work on a “magnetic resonance spectrometer on a

chip” to achieve magnetic-resonance imaging

resolution of 1 nanometer on ferromagnetic thin

films. Recent research includes the development

of new ferromagnetic resonance (FMR) spectrometers based on calorimetry, torque, and

transfer of spin angular momentum. Such sensors

can be integrated with atomic-force microscopes

for imaging of local dc and rf magnetic fields.

Atomic-force microscope (AFM) head adapted for

MEMS magnetometry. The head is placed in a

precision dipole magnet for magnetic-moment

measurements of magnetic films deposited onto

the flat surface of an AFM cantilever. Measurements can be made at fields up to 1.2 teslas.

Customer Needs

The National Storage Industry Consortium recently drafted a recording-head metrology roadmap that calls for high resolution, quantitative

magnetic microscopes and magnetometers that go

beyond the limitations of current technology.

Magnetic measurement systems have become

increasingly complex. Our expertise in magnetism, probe microscopy, and clean-room microfabrication techniques helps move instruments

from the development stage to routine operation

in the industrial laboratory and on the factory

floor.

Cantilever chip mounted near a microstrip resonator. The cantilever, fabricated in the new

MEMS laboratory in Boulder, consists of a bilayer

of silicon nitride and glass with a Ni-Fe FMR

sensor deposited at the tip. Calorimetric detection of FMR occurs when the microwave heat

absorption causes the bilayer to bend.

Industry also looks to NIST for fundamental

constants and representations of magnetic units

as it pushes to smaller time and length scales.

The physics of nanometer-scale magnetism must

be explored so that industry can make the right

choices for recording at densities of over 100

gigabits per square centimeter.

In order to improve upon magnetic force microscopy, our project is focusing on specialized

magnetic-force microscope (MFM) tips for

imaging heads and media. Ultra-small tips are

being developed for magnetic image resolution of

10 nanometers. We are looking at new technologies for making very sharp probe tips and for

controlling nanoscale magnetic structure near the

tip. In addition, more sensitive MFM instruments

are being developed.

Quantitative field mapping of heads and media

Project Leader:

John Moreland

Staff-Years (FY 2000):

1 professional

1 postdoctoral associate

Funding Sources:

NIST (90%)

Other (10%)

Parent Program:

Magnetics
 Magnetics Group 11

can be done with tiny field probes based on

electromechanical detection of magnetic resonance. We are developing ways to attach submicrometer magnetic resonance particles to ultrasensitive cantilevers and to position particles a

few nanometers from the sample surface.

We are developing new tools for measurements

of nanoscale magnetic phenomena and representations of magnetic units for the next generation

of data storage devices. We are developing

MEMS magnetometers with integrated magnetic

samples that can offer tremendous gains in magnetic-moment sensitivity. We have broadened our

clean-room fabrication capabilities to include

MEMS bulk and surface micromachining of Si.

Technical Strategy

Our plans over the next five years are to demonstrate “magnetometers on a chip” based on

MEMS devices that will enable us to create

instruments that have superior performance

compared to current magnetic-measurement

methods. Our new micromachining facility, in

association with the Electromagnetic Technology

Division, is now operational. The facility is at the

state of the art, providing the tools necessary for

bulk and surface micromachining on Si wafers.

Scanning Probe Development

In order to improve upon scanning probe microscopes such as MFM and keep pace with industry

needs, we are focusing on specialized MFM tips

for imaging heads and media. Ultra-small tips are

currently being developed for magnetic-image

resolution of 20 nanometers. We are looking at

new technologies for fabricating, controlling, and

measuring nanometer-scale magnetic structures

near the probe tip. In particular, MFM resolution

can improve only with the development of more

sensitive cantilevers for measuring the small

magnetic forces associated with nanometer-scale

magnetic probe tips.

Conventional MFM is not an intrinsically quantitative technique. However, quantitative field

mapping can be done with tiny field probes based

on mechanical detection of magnetic resonance

in the probe. We are developing ways to fabricate

small magnetic-resonance particles on ultrasensitive cantilevers and position the particles a

few nanometers from the sample surface for field

mapping with 1 nanometer resolution.

MILESTONE: High-frequency scanning probes — 

In 2001, compare capabilities of calorimetric, magneticmoment, and spin-decay scanning ferromagneticresonance (FMR) probes.

MILESTONE: High-frequency scanning probes —

In 2001, develop low-insertion-loss glass/nitride

bimaterial cantilever FMR probes for highresolution microwave power imaging.

MILESTONE: Recording studies — By 2002, develop 

micromachined nitride-membrane substrates for 

new magnetic imaging standard.

MILESTONE: Magnetic resonance imaging

based on MRFM — By 2002, demonstrate force 

sensitivity at the 10-18 newton level with cantilevers

fabricated in the MEMS fabrication facility.

MILESTONE: New MFM technology — In 2001, 

demonstrate sample-on-cantilever MFM.

MEMS Magnetometer Development

We will provide new instruments based on highly

specialized MEMS chips fabricated at NIST. The

instruments will be inexpensive, since MEMS

can be batch-fabricated in large quantities. In

addition, large-scale magnetic wafer properties

can be transferred to smaller MEMS magnetometers so that nanometer-scale measurements

can be calibrated with reference to fundamental

units. In particular, our focus will be the development of torque and force magnetometers,

magnetic-resonance spectrometers, and magnetic-resonance imaging (MRI) microscopes on

MEMS chips. Over the long term, we expect that

this technology will lead to atomic-scale magnetic instrumentation for the measurement and

visualization of fundamental magnetic phenomena.

MILESTONE: Fabrication and integration — In 2001,

optimize micro-torsional oscillator fabrication

process for quantitative measurements with the

micro-resonating torque magnetometer.

MILESTONE: Fabrication and integration — In 2001,

demonstrate magnetic force and torque sensors

with a sensitivity of 10-18 ampere meter squared

per root hertz.

MILESTONE: Magnetic moment measurements —

In 2001, demonstrate in-situ monitoring of thin-film

magnetic moment during deposition.

MILESTONE: Magnetic moment measurements —

By 2002, demonstrate in-situ monitoring of thin 

films with sub-monolayer (tenth nanometer)

sensitivity.

MILESTONE: Spin-decay measurements — In 

2001, develop torsion oscillators with isolated 

sub-micrometer magnetic dots.

MILESTONE: Magnetic resonance imaging

based on a MEMS sensor — By 2003, develop highgradient, miniature electromagnets and rf coils.

I have been

impressed by the

research on

ferromagnetic

resonance imaging

and development of

multipurpose

scanning probes.

These probes can be

used for high accuracy

magnetometry and

the measurement of

angular momentum of

rf magnetic fields.

Prof. Isaak Mayergoyz

University of Maryland
 12 Electronics and Electrical Engineering Laboratory

Accomplishments

! New Scanning-Probe Microscope for Quantitative High-Resolution Imaging of Magnetic

Fields in Magnetic Recording — The technique

is based on technology recently developed in

several laboratories in the U.S. and abroad for a

new type of probe microscopy referred to as

“magnetic-resonance force microscopy”

(MRFM). High-resolution field mapping with an

MRFM instrument relies on the combination of a

small magnetic-resonance particle mounted on an

atomic force cantilever that constitutes a very

sensitive probe of local magnetic fields near a

magnetic device. Magnetic-resonance phenomena are the basis for the most accurate measurements of magnetic fields.

MRFM image of a magnetic field contour line

above a small permanent magnet. The dimensions of the scanning probe (shown in the inset

at the lower left) determine the resolution of the

contour line image (3.4 micrometers). The probe

is a diphenyl-picrylhydrazyl (DPPH) particle with

a strong, narrow electron-spin resonance (ESR)

absorption line. The scanned area is 40 micrometers by 40 micrometers.

! New Ferromagnetic Resonance (FMR)

Spectrometers Based on Micromechanical Sensors for Measurements of Magnetic Thin Films

— The MEMS FMR spectroscopy probes are

based on calorimetry, torque, and angularmomentum absorption. The sensors can be integrated into an atomic-force microscope for imaging local dc and rf magnetic fields. Spectra

show a peak in the cantilever deflection as a

function of applied magnetic field. This corresponds to a peak in the absorbed microwave

power that occurs under FMR conditions for a

given ferromagnetic film. The techniques are

being investigated as potentially superior ways to

make quantitative measurements of the saturation

magnetization of thin-film samples with very

small total magnetic moments.

Cantilever vibration caused by heating versus

applied field for a 30 nanometer Co film at different relative input microwave power levels. Detection is based on the different thermal expansion coefficients of the Co film and the Si cantilever that cause the cantilever to bend when

heated. The microwave power is chopped at 1

kilohertz in order to vibrate the cantilever. The

data show the characteristic Lorentzian absorption line expected for FMR in Co.

! Micromechanical Detection of Energy and

Angular Momentum Transfer in Ferromagnetic

Resonance — A spinning top in a gravitational

field undergoes precession. Similarly, a magnetization vector in a magnetic field precesses. For

the precession to persist, microwave energy

perpendicular to the static magnetic field must be

supplied to the ferromagnetic material. In FMR,

the natural damping of the precessional motion of

magnetic spins in FMR results in a transfer of

both energy and angular momentum to the crystal

lattice of the ferromagnetic specimen. Absorption

of the energy results in heating of the material,

whereas transfer of the spin angular momentum

results in a torque on the material. The source of

the energy and angular momentum can be traced

to the energy and angular momentum of the

microwave photons that induce the resonance.

This is one example of new micro-cantileverbased methods of magnetic metrology developed

at NIST and the first demonstration of torque

detection from angular momentum absorption in

FMR.
 Magnetics Group 13

Cantilever torque and power absorption as a

function of applied field for a 30 nanometer Ni-Fe

film deposited onto a Si cantilever. The torque is

caused by the decay of spin angular momentum

when FMR occurs in the film. By measuring the

power-torque ratio as a function of resonance

field, it may be possible to directly measure the

saturation magnetization of a magnetic film

without a priori knowledge of the gyromagnetic

constant or the volume of the material.

! Static Magnetic Field Imaging Based on

FMR Scanning Probe — A Ni-Fe thin film probe

patterned on the end of an atomic-forcemicroscope (AFM) cantilever is excited by FMR

with microwaves from a stripline. Mechanical

detection of FMR allows for the quantitative

determination of local fields as the probe is

scanned over the sample surface. The NIST

instrument has demonstrated calibrated, twodimensional magnetic-field mapping with lateral

resolution of approximately 20 micrometers and

field sensitivity of 50 amperes per meter. Several

scanned-probe magnetic-imaging techniques

based on the principles of AFM have been developed in the past decade. The most popular of

these has been the magnetic-force microscope,

because of its high resolution, simplicity, and

robustness. However, it has proven difficult to

quantify MFM results because the instrument

images field gradients rather than fields. A calibration source with well-characterized field

gradients on a 10 nanometer scale is needed to

calibrate the response. Other scanned-probe

techniques have been developed that are directly

field sensitive. These use magnetoresistors,

superconducting quantum interference devices,

and Hall-effect sensors that can be calibrated

with uniform magnetic fields. However, these

sensors do not scale easily to sub-micrometer

dimensions, and they require electrical connections, which makes it difficult to integrate them

to the tip of a cantilever. Techniques that use

mechanical detection eliminate the need to fabricate complex structures on the end of a cantilever.

! Microwave Scanning Probe Based on Mechanical Detection Ferromagnetic Resonance —

The probe described above for static magnetic

field measurements can also be used to measure

microwave magnetic fields near microwave

components. The local field measurements can be

used to determine the current distribution in such

devices. The probe is based on the bimaterial

calorimeter affect. A special cantilever has been

developed in our MEMS fabrication facility

designed specifically for these measurements. It

is a rectangular beam, 1 micrometer by 50 micrometers by 500 micrometers, consisting of

glass and silicon-nitride films deposited by lowpressure chemical-vapor deposition (LPCVD).

These cantilevers have low rf losses compared to

their Si predecessors and are therefore less intrusive as field probes.

Line scan over a microstrip resonator showing

the variation of a 10 gigahertz microwave field

HRF as a function of position. Resolution is determined by the size of the FMR Ni-Fe probe, about

10 micrometers.

! First Micromachined Structures in New

MEMS Facility — We have fabricated cantilevers and beams using a surface micromachining

processes in which structures are made by patterning a low-stress nitride film on a sacrificial

low-temperature oxide film grown on Si wafers.

The cantilevers and beams are used to measure

nonuniform and linear residual stress in the films

to make sure the furnace reactor deposition

process is within specifications. In addition, we

fabricated Si cantilevers with a bulk micromachining process based on a silicon-nitride etch

mask for anisotropic potassium-hydroxide etch.

A series of cantilevers and T-bar torsional oscillators were fabricated for MEMS magnetometer

applications. The furnace reactors provide the

basic tools for both surface and bulk micromachining on Si wafers. The furnaces are capable
 14 Electronics and Electrical Engineering Laboratory

of five processes, including dry and wet oxidation, boron doping, silicon-nitride deposition,

polysilicon deposition, and low-temperature

silicon-oxide deposition. Thermal oxides are

useful as wet etch masks, insulators, and as

structural material for cantilevers. Boron doping

is useful as an etch stop for bulk micromachining.

Silicon nitride is useful as an etch mask and as a

structural material. The nitride process can be

adjusted by varying the ratio of the reactive gases

dichlorosilane and ammonia.

Scanning-electron micrograph of a series of

silicon-nitride cantilevers for MEMS magnetometer. Processes available for surface and bulk

micromachining include wet and dry oxidation,

boron diffusion doping, and LPCVD of silicon

nitride, polysilicon, and low-temperature oxide

(glass).

Films of silicon nitride have very low residual

stress and are useful for making extremely thin

cantilevers (less than 50 nanometers thick) required for applications such as the MRFM, where

force sensitivity at the 10-18 newton level is

needed. Polysilicon films are useful as sacrificial

layers for surface micromachining of silicon

nitride. Polysilicon is also the choice for structural material in micromachined actuators such as

electrostatic comb drives. Finally, the furnaces

can grow sacrificial films of low-temperature

oxide that are etched relatively quickly in hydrofluoric acid.

Recent Publications

A. Jander, J. Moreland, and P. Kabos, “Angular Momentum

and Energy Transferred through Ferromagnetic Resonance,”

submitted.

A. Jander, P. Kabos, and J. Moreland, “Magnetic Field

Imaging with a Scanning Ferromagnetic Resonance Probe,”

submitted.

J. Moreland, P. Kabos, A. Jander, M. Löhndorf, R.

McMichael, and C.-G. Lee, “Micromechanical Detectors for

Ferromagnetic Resonance Spectroscopy,” Proc. SPIE 4176:

Micromachined Devices and Components VI, Eric Peters and

Oliver Paul, Eds., 84-95 (September 2000).

J. Moreland, M. Löhndorf, P. Kabos, and R. D. McMichael,

“Ferromagnetic Resonance Spectroscopy with a Micromechanical Calorimeter Sensor,” Rev. Sci. Instrum. 8, 3099-

3103 (August 2000).

M. Löhndorf, J. Moreland, P. Kabos, and N. D. Rizzo,

“Microcantilever Torque Magnetometry of Thin Magnetic

Films,” J. Appl. Phys. 87, 5995-5997 (May 2000).

M. Löhndorf, J. Moreland, and P. Kabos, “Ferromagnetic

Resonance Detection with a Torsion-Mode Atomic-Force

Microscope,” Appl. Phys. Lett. 76, 1176-1178 (February

2000).

T. G. Ruskell, M. Löhndorf, and J. Moreland, “Field Mapping

with the Magnetic Resonance Force Microscope,” J. Appl.

Phys. 86, 664-670 (July 1999).
 Magnetics Group 15

Magnetic Thin Films and Devices

Project Goals

This project develops measurements and standards for magnetic thin-film materials and devices for the magnetic data storage and magnetoelectronics industries, with applications in magnetic recording, magnetic solid-state memories,

magnetic sensors, and magnetic microwave

devices. The emphasis is on the performance of

nanoscale devices, consisting of multilayer and

multicomponent thin-film systems, at microwave

frequencies. Project members have successfully

devised ways to control the dynamical properties

of magnetic devices. In addition, they fabricate

magnetic nanostructures to determine the resolution of magnetic imaging systems and develop

new combinatorial materials and on-wafer metrology. Recently, the project has begun to develop new techniques to measure spin-dependent

electron transport at surfaces and interfaces in

advanced magnetic device structures. Long-term

goals include the development of metrology that

will be required to develop quantum spin-based

electronics for data storage and terahertz information processing.

High-resolution magnetic force micrograph of

bits in the magnetic imaging reference standard.

The area of the image is 4 micrometers on a side.

Customer Needs

Our project serves the needs of U.S. industries

that use and develop magnetic thin-film and

magnetic-device technologies. These industries

include magnetic-hard-disk recording, magnetic

tape recording, magnetic random-access memories (MRAM), and magneto-electronics (including sensors, isolators, and microwave devices).

The data storage and magneto-electronics industries are pushing toward smaller and faster technologies that require sub-micrometer magnetic

structures to operate in the gigahertz regime.

New techniques are required to measure and

characterize these magnetic structures. Advances

in technology are dependent on the discovery and

characterization of new effects such as giant

magnetoresistance and spin-dependent tunneling.

A detailed understanding of spin-dependent

transport is required to optimize these effects and

to discover new phenomena that will lead to new

device concepts.

Magnetic thin film systems have become increasingly complicated, often containing quaternary alloys or multilayer systems with 4 to 10

elements that require atomic-level control of the

layers. New techniques are required to efficiently

and systematically develop and characterize the

magnetic, electronic, and mechanical properties

of these advanced thin-film systems. In particular, new metrological systems are required that

will be capable of making on-wafer measurements on a large number of sites over a large

region of parameter space.

Technical Strategy

We are developing several new techniques to

address the needs of U.S. industries that require

characterization of magnetic thin films and device structures on nanometer-size scales and

gigahertz frequencies.

We have fabricated magnetic nanostructures that

can be used to determine the resolution and

relative merits of various magnetic imaging

systems. These structures include bits recording

on commercial media, small Co-Pt nanostructures fabricated by electron-beam lithography,

and small structures fabricated by focused-ionbeam techniques. The magnetic structures must

have stable, well-characterized features on length

scales down to 10 nanometers to allow the testing

of commercial imaging systems.

MILESTONE: During 2001-2002, develop ballistic

electron magnetic microscopy (BEMM) to characterize

magnetic devices at 10 nanometer length scales.

We have fabricated test structures that allow the

characterization of small magnetic devices at

frequencies up to 10 gigahertz. The response of

sub-micrometer magnetic devices, such as spinvalves, magnetic tunnel junctions, and giantmagnetoresistive devices with current perpendicular to the plane, have been characterized both

in the linear-response and the non-linear switchProject Leader:

Stephen Russek

Staff-Years (FY 2000):

1 professional

1 postdoctoral associate

1 graduate student

Funding Sources:

NIST (50%)

Other (50%)

Parent Program:

Magnetics
 16 Electronics and Electrical Engineering Laboratory

ing regimes. The linear-response regime is used

for magnetic recording read sensors and highspeed isolators, whereas the switching regime is

used for writing or storing data. Measured data

have been compared to numerical simulations of

the device dynamics to determine the ability of

current theory to predict the behavior of magnetic

devices.

MILESTONE: In 2001, characterize gigahertz

noise and thermal-fluctuation-induced 

dynamics in 100 nanometer spin valves and 

tunnel junctions.

We are developing new techniques to measure

the electronic and magnetic properties of magnetic thin-film systems in situ (as they are deposited). One such technique, in-situ magnetoconductance measurements, can determine the

effects of surfaces and interfaces on spindependent transport in a clear and unambiguous

manner. The effects of sub-monolayer additions

of oxygen, noble metals, and rare earths on giant

magnetoresistance have been studied.

MILESTONE: During 2001-2002, investigate the 

electronic scattering from nano-oxides in giant

magnetoresistive (GMR) systems and determine

if electron confinement techniques can

significantly enhance read-head sensor

performance.

We are developing combinatorial materials

techniques to assist industry in the development

and characterization of complicated magnetic

thin-film systems. Combinatorial materials techniques involve the fabrication of libraries with a

large number of sites with systematic variation of

materials properties such as composition, or

process parameters such as growth temperature.

In addition to library fabrication, the combinatorial process involves the development of highthroughput on-wafer metrologies that can systematically characterize the libraries and scan for

desirable materials properties.

MILESTONE: By 2002, develop techniques to make 

on-wafer measurements of saturation magnetization

and magnetostriction.

Finally, we are exploring new physical effects to

create the foundation to develop entirely new

technologies relying on spin-dependent transport

at the quantum level. We are investigating the use

of spin-momentum transfer to induce a dynamical response for microwave and high-speed

signal processing systems. We are investigating

methods of measuring small numbers of spins in

semiconductor devices and spin traps. Developing this metrology will be an essential ingredient

to the development of methods to control and

High-speed test circuits are used to measure the performance of giant-magnetoresistance and spindependent tunneling devices at frequencies up to 10 gigahertz.

Our association with

your group has been

highly successful.

Your work on

magnetic switching is

extensive and

important. The

measurements and

analysis on the

samples we sent was

very much

appreciated.

Dr. Jim Daughton

President

Nonvolatile Electronics, Inc.
 Magnetics Group 17

manipulate small numbers of spins in a spin

circuit.

MILESTONE: By 2002, measure spintransfer-induced dynamics in nanoscale 

current-perpendicular-to-plane (CPP) devices 

in collaboration with Cornell University 

and Motorola.

MILESTONE: In 2001, measure electron spin

resonance (ESR) in sub-micrometer spinpolarized two-dimensional degenerate

electron-gas devices.

Accomplishments

! We have measured the ferromagnetic resonance in micrometer-sized spin-valve devices.

The ferromagnetic resonance was measured using

both time-domain and frequency-domain magnetoresistance techniques. This work represents

the measurement of ferromagnetic resonance in

the smallest single particle to date. The work

provides a clear measurement of the response of

magnetic sensors similar to those used in magnetic recording read heads, up to 6 gigahertz.

Knowledge of the high-frequency performance of

these devices will be required in the next few

years when the data transfer rates exceed 1 gigahertz. This work has further stimulated the use of

these sensors in other magneto-electronic applications such as high-speed isolators working in

the gigahertz regime.

! We have completed a study of switching

probabilities in small spin-valve devices designed

for MRAM applications. The switching probability was measured as a function of magnetic

field pulse height and pulse width. At long pulse

widths (above 1 nanosecond) reproducible

switching, with unity switching probability, was

observed. As the pulse width was decreased, a

rapid transition occurred in which the switching

probability decreased from 1 to 0 over a span of

100 picoseconds. Metastable states were observed in this transition region. The metastable

states were found to have a very wide spread in

lifetimes, ranging from a few nanoseconds to

several milliseconds.

! Using micromagnetic simulations of rotations in spin-valve devices, we have shown that

the inclusion of disorder causes a non-uniform

damping, which agrees qualitatively with the

measured data from small spin-valve devices.

The simulations showed that during the initial

Time- and frequency-domain measurements of the ferromagnetic resonance in a micrometer-sized

spin-valve device.
 18 Electronics and Electrical Engineering Laboratory

large-angle motions there was a larger transfer of

energy, mediated by the disorder, from the uniform mode to short-wavelength magnetic modes.

As the motion amplitude decreased, fewer spin

waves were produced and the damping decreased. The exact type of the disorder in giantmagnetoresistive devices remains to be determined. Possible candidates include edge roughness, Néel coupling with the pinned layer, variations in local anisotropy, or stress.

! We discovered a new method of engineering

the high-speed dynamical properties of technologically relevant magnetic thin films. Doping

Ni-Fe films with a few percent of Tb will increase the damping of the films by an order of

magnitude while not appreciable changing other

magnetic properties. Gd doping was also explored and showed less increase in damping. Gd

has only a spin moment whereas Tb has both a

spin and an orbital moment. The results are

Micromagnetic simulation of response of 0.8 micrometer by 4.8 micrometer spin-valve device to a 150

picosecond, 80 millitesla, transverse field pulse.

Magnetic force microscope image of Co-Pt multilayer dots, 100 nanometers in diameter.

Magnetic combinatorial library showing 2

millimeter sites with identification numbers.
 Magnetics Group 19

consistent with the hypothesis that the orbital

moment of Tb, in combination with the high

anisotropy of the orbitals, allows the magnetization to directly couple to the lattice. Both uniform

and modulation doping were explored. Temperature-dependent measurements of the magnetization and damping were made, along with

high-resolution x-ray measurements, to determine

the correlation of the damping to the magnetic

properties and microstructure. This work represent the first effort to engineer the intrinsic dynamical properties of materials used in magnetic

data storage applications.

! We measured magnetic-force microscope

line scans of 100 nanometer Co-Pt dots and

compared them with calculated field and fieldgradient profiles. The calculations show that

there should be sharp features in the field gradients at the edge of the dots if the dots were ideal,

with uniform perpendicular magnetization. The

features should have peak widths of about 20

nanometers, which were not resolved in our

measurements. Therefore, the calculations indicate that these samples may be useful for magnetic imaging reference samples, since they

should have features at or beyond the resolution

of current magnetic-force microscopes.

! We completed fabrication of the first set of

magnetic combinatorial libraries in collaboration

with the Materials Science and Engineering

Laboratory. The libraries cover a large range of

the Tb–Ni-Fe–Co phase diagram and contain

several magnetic and crystalline phases. The

magnetic structure ranges from in-plane ferromagnetic to perpendicular ferrimagnetic to isotropic ferrimagnetic, to paramagnetic. These

libraries were designed to explore giantmagnetostrictive materials and to provide test

systems for developing on-wafer magnetic metrology.

! We completed a study of the high-speed

magnetic switching properties of Co-Fe-Hf-O in

collaboration with Nonvolatile Electronics, Inc.

Co-Fe-Hf-O is a new material developed by NVE

with potential applications in high-speed magnetic devices. Co-Fe-Hf-O has a tunable resistivity and anisotropy and has dynamic properties

that exceed those of Ni-Fe for thicknesses greater

than 100 nanometers.

Recent Publications

S. E. Russek, P. Kabos, T. J. Silva, F. B. Mancoff, D. Wang,

Z. Qian, and J. M. Daughton, “High Frequency Measurements

of CoFeHfO,” submitted.

S. E. Russek, W. E. Bailey, and G. Alers, “Magnetic Combinatorial Thin-Film Libraries,” submitted.

W. E. Bailey, P. Kabos, F. B. Mancoff, and S. E. Russek,

“Control of Magnetization Dynamics in Ni80Fe20 Thin Films

Through the Use of Rare-Earth Dopants,” IEEE Trans.

Magn., to be published.

S. E. Russek and S. Kaka, “Time and Frequency Domain

Measurements of Ferromagnetic Resonance in Small SpinValves,” IEEE Trans. Magn., in press.

S. E. Russek and W. E. Bailey, “Magnetic Domain Structure

and Imaging of Co-Pt Multilayer Thin-Film Nanostructures,”

IEEE Trans. Magn., in press.

P. Kabos, S. Kaka, S. E. Russek, and T. J. Silva, “Metastable

States in Large Angle Magnetization Rotations,” IEEE Trans.

Magn., in press.

S. E. Russek, S. Kaka, and M. J. Donahue, “High-Speed

Dynamics, Damping, and Relaxation Times in Submicrometer Spin-Valve Devices,” J. Appl. Phys. 87, 7070-7072 (May

2000).

S. Kaka and S. Russek, “Switching in Spin-Valve Devices in

Response to Subnanosecond Longitudinal Field Pulses,” J.

Appl. Phys. 87, 6391-6393 (May 2000).

S. E. Russek, J. O. Oti, and Y. K. Kim, “Switching Characteristics of Spin Valve Devices Designed for MRAM Applications,” J. Magn. Magn. Mater. 198-199, 6-8 (July 1999).

S. E. Russek, T. M. Crawford, and T. J. Silva, “Study of

NiFe/Al/Al2O3 Magnetic Tunnel Junction Interfaces Using

Second-Harmonic Magneto-Optic Kerr Effect,” J. Appl. Phys.

85, 5273-5275 (April 1999).

P. Rice and S. E. Russek, “Observation of the Effects of Tip

Magnetization States on Magnetic Force Microscopy Image,”

J. Appl. Phys. 85, 5163-5165 (April 1999).

S. E. Russek, J. O. Oti, S. Kaka, and E. Y. Chen, “High Speed

Characterization of Submicrometer Giant Magnetoresistive

Devices,” J. Appl. Phys. 85, 4773-475 (April 1999).
 20 Electronics and Electrical Engineering Laboratory

Standards for Superconductor

Characterization

Project Goals

This project develops standard measurement

techniques for critical current and provides quality assurance and reference data for commercial

high-temperature and low-temperature superconductors. Applications supported include magnetic-resonance imaging, research magnets, faultcurrent limiters, magnetic energy storage, magnets for fusion confinement, motors, generators,

transformers, transmission lines, magnets for

crystal growth, and superconducting bearings.

Project members assist in the creation and management of international standards for superconductor characterization covering all commercial

applications, including electronics. The project is

currently focusing on critical-current measurements of marginally stable superconductors, on

temperature-variable critical-current measurements, and on measuring the irreversible effects

of changes in magnetic field and temperature on

critical current.

Magnetic resonance imaging (MRI) system in a

hospital setting. A superconducting magnet is

used to produce a high magnetic field, which is

one of the necessary components for imaging

without using ionizing radiation. The inset shows

a cross section of the patient’s knee. Photo

courtesy of Philips Medical Systems.

Customer Needs

We serve the U.S. superconductor industry,

which consists of many small companies with

limited resources for committing to the development of new metrology and standards. We participate in projects sponsored by other government agencies that involve U.S. industry, universities, and national laboratories.

The potential impact of superconductivity on

power systems makes this technology very important. We focus on (1) developing new metrology needed for evolving, large-scale superconductors, (2) participating in interlaboratory comparisons needed to verify techniques and systems

used by U.S. industry, and (3) developing international standards for superconductivity needed

for fair and open competition and improved

communication.

Technical Strategy

This project’s primary activities are criticalcurrent measurement metrology, interlaboratory

comparisons, and development of international

standards. One of the most important performance parameters for large-scale superconductor

applications is the critical current. Critical current

is difficult to measure correctly and accurately;

thus, these measurements are often subject to

scrutiny and debate.

With each significant advance in superconductor

technology, new procedures, interlaboratory

comparisons, and standards are needed. International standards for superconductivity are created

through the International Electrotechnical Commission (IEC), Technical Committee 90

(TC 90).

MILESTONE: During 2001-2003, continue to manage 

and help create international standards for

superconductivity.

The next generation of Nb3Sn and Nb3Al wires is

pushing towards higher current density, less

stabilizer, larger wire diameter, and higher magnetic fields. The resulting higher current required

for critical-current measurements turns many

minor problems into significant engineering

challenges. For example, specimen heating, from

many sources, during the measurement can cause

a wire to appear to be thermally unstable.

MILESTONE: In 2001, study the effect of extrinsic

parameters on overall stability of Nb3Sn wires

during routine testing to 1000 amperes in a

magnetic field of 12 teslas.

MILESTONE: By 2002, determine a procedure for 

routine critical-current measurements up to 1500

amperes at fields of 12 teslas.

Project Leader:

Loren Goodrich

Staff-Years (FY 2000):

1 professional

1 technician

Funding Sources:

NIST (85%)

Other (15%)

Parent Program:

Power
 Magnetics Group 21

MILESTONE: In 2001, complete a detailed 

report on variable-temperature critical-current

measurements of high-temperature

superconductors.

Accomplishments

! Critical-Current Tutorial — We gave an

invited tutorial during the 2000 Applied Superconductivity Conference on critical-current

measurements for power applications. The procedure consists of measuring the voltage-current

characteristic and applying a criterion to determine the critical current. The figure below shows

an illustration of the voltage-current characteristic and two criteria. Typical criteria are electricfield strength of 10 microvolts per meter and

resistivity of 10-14 ohm meters.

DC current (arbitrary units)

0

Voltage (arbitrary units)

0

1

c V = I L /S

V=LE c

 V =I L/S c c

1

V =LE c c

ρ

ρc

Illustration of a superconductor’s voltage-current

characteristic with two common criteria applied.

An actual voltage-current characteristic for a

Nb-Ti wire is shown below.

0 100 200 300

I (A )

0

1 0

2 0

3 0

V (μV)

V c

I c=297.4 A

260 300 320 I (A)

0.01

0.10

1.00

10.00

V (μV)

Full-logarithm ic plot

Vc

I c

=297.4 A

Fit n=55.7

The voltage-current characteristic of a Nb-Ti wire

in a magnetic field of 2 teslas. The critical current

Ic is determined. The corresponding voltage Vc =

Ec⋅L = 5 microvolts when Ec =10 microvolts per

meter and the voltage tap separation L = 0.5

meters. The inset is a plot of these same data on

a logarithmic scale.

This curve is much steeper than in the above

illustration. Typically, the curve can be approximated by the equation V = V0 (I/I0)

n

, where V0, I0,

and the n-value are constants. The n-value is the

slope of the voltage-current curve when plotted

on a logarithmic scale (see inset in the plot).

! Performance of Wire Verified — A national

laboratory involved in the U.S. effort for the

international Large Hadron Collider program

asked us to conduct critical-current verification

on several Cu/Nb-Ti wires. The critical-current

specification was 1925 amperes at 5 teslas. The

current density in the Nb-Ti is over 3000 amperes

per square centimeter. These wires were designed

with only the minimum amount of Cu stabilizer,

which made them difficult to measure. The

application will use a cable constructed of these

wires and additional high-purity aluminum stabilizer will be added to the cable to make the application more stable. We tested 44 specimens from

about 528 km of wire so far in the program. The

distribution of critical currents is shown in the

plot below. Most of the specimens tested above

the specification. The lowest value on one specimen was found to be caused by an end effect.

Our resistivity measurement at room temperature

indicated that the copper fraction of this specimen was higher than in all the other specimens,

which is consistent with a lower critical current.

With this observation, the manufacturer was able

to crop one end of the wire. A new specimen was

tested and found to be above the critical-current

specification, which saved about 11 kilometers of

wire from rejection. This is one example of how

we help solve some of the measurement problems

facing the U.S. superconductor wire industry.

Our experience with such measurements will

help in making future standards more practical.

1840 1920 2000 2080

Critical Current (A )

0

2

4

6

8

Number of occurences





























































The distribution of critical-current measurements

on 44 specimens of Nb-Ti wire at 10 microvolts

per meter, 5 teslas, and 4.2 kelvins.

We are in debt to

Loren Goodrich for his

work with our

conductor samples,

and we have profited

greatly from his

general knowledge of

materials of this type.

Dr. Richard P. Smith

Fermilab
 22 Electronics and Electrical Engineering Laboratory

! Variable-Temperature Measurements of

Critical Current — We recently developed and

tested a new variable-temperature critical-current

measurement system. We used this system to

measure commercially produced Ag-sheathed

Bi2Sr2Ca1Cu2Ox and Bi2Sr2Ca2Cu3Ox multifilamentary tapes to currents over 250 amperes.

The critical currents of these high-temperature

superconductor tape samples depend on the angle

of the applied magnetic field relative to the c-axis

of the material.

H @ 90°

c-axis

tap e sp ecim en

current

H @ 0°

Illustration of the definition of magnetic field

angle relative to the c-axis of the material.

B i-2223

0°, 0.1 μ V /cm

0.01 0.10 1.00 10.00

μ 0H (T)

0

5 0

100

150

200

250

300

350

Ic (A )

4 K

10 K

20 K

35 K

50 K

65 K

80 K

(b)

Bi-2223

90°, 0.1 μ V /cm

0.01 0.10 1.00 10.00

μ 0H (T)

0

5 0

100

150

200

250

300

350

Ic (A )

4 K

10 K

20 K

35 K

50 K

65 K

80 K

(a)

Critical current as a function of magnetic field

sweep for an Ag/Bi2Sr2Ca2Cu3Ox tape at various

temperatures and two angles: (a) 90°, (b) 0°.

The definition of this angle is given in the illustration. The data plots show the measured critical

current of a Bi2Sr2Ca2Cu3Ox specimen as a function of field and at various temperatures and two

angles. A short paper on these results was presented at the 2000 Applied Superconductivity

Conference. A longer paper is currently in the

review process.

! Sixth IEC Meeting on Superconductivity —

We organized, hosted, and participated in the

sixth meeting of IEC Technical Committee 90

(TC 90) on superconductivity in Boulder, Colorado. The meeting allowed experts from around

the world to come together and work to advance

the draft international standards in six Working

Groups. In addition, results from pre-standards

research and interlaboratory comparisons were

presented on four new working drafts and on six

future drafts. To date, two IEC measurement

standards have been published and a third standard on superconductivity vocabulary is being

published. As a result of this meeting, three more

draft standards are now ready for the final voting

stage. Information about the IEC TC 90 activities

can be found at http://www.IEC.ch/ dashbd-e.htm

(enter “90” for the committee number). An outline of the organization is given below.

IEC Technical Committee 90

Secretariat Japan

Chairman L. F. Goodrich

Secretary K. Sato

Participating Countries 11

Observing Countries 18

TC 90 Working Groups

1 Terms and Definitions (301 terms, 110 pp., in press)

2 Critical-Current Measurement of Cu/Nb-Ti (43 pp.,

published)

3 Critical-Current Measurement of Bi-Based Superconductors

4 Residual Resistivity of Cu/Nb-Ti

5 Room Temperature Tensile Tests of Cu/Nb-Ti

6 Matrix Composition Ratio of Cu/Nb-Ti

7 Critical-Current Measurement of Nb3Sn (57 pp., published)

8 Electrical Characteristic Measurements, Surface Impedance

9 AC Losses in Cu/Nb-Ti

! Resistivity of High-Purity Cu — We measured residual resistivity ratio (RRR) measurements of four high-purity Cu samples (for a total

of 35 for this program) from an aerospace company. The RRR measurements are used to esti-
 Magnetics Group 23

mate the low temperature thermal conductivity of

thermal straps to be used in several instruments

for the Space Infrared Telescope Facility.

! Critical Current of Nb-Ti — We measured

critical currents of three Nb-Ti conductors from a

U.S. wire manufacturer. The currents required

were beyond the capabilities of their measurement facilities. The company has an occasional

need for some measurements at high current

(2000 amperes) or high field (12 teslas). Ours is

one of the few labs in the country that can do

these measurements.

Ted Stauffer and Loren Goodrich lowering a test

fixture into a critical current measurement cryostat. The cloud at the top of the cryostat results

from the boiling cryogen.

! Suppression of Flux Jumps — We demonstrated that flux jumps could be suppressed

during the measurement of hysteresis loss by

immersing marginally-stable Nb3Sn conductors

in liquid He. The increased thermal conduction

affords dynamic stability against flux jumps,

which allows ac losses to be estimated from the

area of the magnetization-versus-field loop.

! Standards Committees — Loren Goodrich

was the Chairman of IEC/TC 90, the U.S. Technical Advisor to TC 90, the Convener of Working

Group 2 (WG2) in TC 90, the primary U.S.

Expert to WG4, WG5, and WG6, and the secondary U.S. Expert to WG1, WG3, and WG7. Ted

Stauffer was Administrator of the U.S. Technical

Advisory Group to TC 90.

Recent Publications

L. F. Goodrich and T. C. Stauffer, “Hysteresis in Transport

Critical-Current Measurements of Oxide Superconductors,”

IEEE Trans. Appl. Supercond., in press.

R. B. Goldfarb, L. F. Goodrich, T. Pyon, and E. Gregory,

“Suppression of flux jumps in marginally stable niobium-tin

superconductors,” IEEE Trans. Appl. Supercond., in press.

L. F. Goodrich “III-2: Intercomparison Program in USA. Part

1: Ic Comparison,” submitted to Cryogenics, VAMAS

Supplement.

L. F. Goodrich “III-2: Intercomparison Program in USA. Part

2: Simulator Round Robin Test,” submitted to Cryogenics,

VAMAS Supplement.

L. F. Goodrich “II-4: Critical Current Measurement Methods

for Oxide Superconductor Tapes and Wires. Part 1: Transport

Current Method,” submitted to Cryogenics, VAMAS Supplement.

L. F. Goodrich, L.T. Medina, and T.C. Stauffer, “High

Critical-Current Measurements in Liquid and Gaseous

Helium,” Adv. Cryo. Eng. (Materials), 44, 873-880 (November 1998).

IEC/TC 90, “Superconductivity − Part 2: Critical Current

Measurement − DC Critical Current of Nb3Sn Composite

Superconductors,” International Electrotechnical Commission, International Standard IEC 61788-2 (March 1999).

IEC/TC 90, “Superconductivity − Part 1: Critical Current

Measurement − DC Critical Current of Cu/Nb-Ti Composite

Superconductors,” International Electrotechnical Commission, International Standard IEC 61788-1 (February 1998).
 24 Electronics and Electrical Engineering Laboratory

Superconductor Electromagnetic

Measurements

Project Goals

This project specializes in measurements of the

effect of mechanical strain on superconductor

properties for applications in magnetics, power

transmission, and electronics. Recent research

has produced the first electromechanical data for

the new class of flexible high-temperature superconductors, one of the few new technologies

expected to have an impact on the large electric

power industry and the next generation of accelerators for high-energy physics. The Strain Scaling Law, previously developed by the project for

predicting the axial-strain response of superconductors in high magnetic fields, is now being

generalized to three-dimensional stresses for use

in finite-element design of magnet structures.

Recent research also includes extending the highmagnetic-field limits of electromechanical measurements for development of 23.5 tesla nuclear

magnetic resonance spectrometers operating at 1

gigahertz. The project’s research, which previously led to the first four-contact patents for high

temperature superconductors, is being broadened

to develop electrical contacts with ultra-low

interface resistivity for coated high-temperature

superconductors.

Najib Cheggour, Cam Clickner, and Jack Ekin

preparing to measure the electromechanical

properties of a superconductor tape.

Customer Needs

The project serves industry primarily in two

areas. First is the need to develop a reliable

measurement capability in the severe environment of superconductor applications: low temperature, high magnetic field, and high stress.

The data are being used, for example, in the

design of superconducting magnets for the magnetic-resonance imaging (MRI) industry, which

contributes 2 billion dollars per year to the U.S.

economy.

The second area is to provide data and feedback

to industry for the development of high performance superconductors. This is especially exciting

because of the recent deregulation of the electric

power utilities and the attendant large effort

being devoted to developing reliable superconductors for power conditioning and enhanced

power transmission capability. We have received

numerous requests, both from industry and from

government agencies representing industrial

suppliers, for reliable electromechanical data to

help guide their efforts in research and development in this critical growth period.

The recent success of the second generation of

high-temperature superconductors has brought

with it a new set of measurement problems in

handling these brittle conductors. We have the

expertise and equipment to address these problems.

Technical Strategy

Our project has a long history of unique measurement service in the specialized area of electromechanical metrology. Significant emphasis is

placed on an integrated approach. We provide

industry with first measurements of new materials, specializing in cost-effective testing at currents less than 1000 amperes. Consultation is also

contributed to industry on developing their own

measurements for routine testing. We also provide consultations on metrology to the magnet

industry to predict and test the performance of

very large cables with capacities on the order of

10 000 amperes, based on our tests at smaller

scale. In short, our strategy has consistently been

to sustain a small, well connected team approach

with industry.

We have developed an array of specialized measurement systems to test the effects of mechanical

Project Leader:

Jack Ekin

Staff-Years (FY 2000):

1 professional

1 technician

1 guest scientist

Funding Sources:

NIST (40%)

Other (60%)

Parent Program:

Power
 Magnetics Group 25

stress on the electrical performance of superconducting materials. The objective is to simulate the

operating conditions to which a superconductor

will be subjected in magnet applications. Among

these measurement systems are apparatus for

measuring the effects of axial tensile stress and

transverse compressive stress, and a unique

system for determining the electromechanical

properties of reinforced superconducting composite coils.

These measurements are an important element of

our ongoing work with the U.S. Department of

Energy (DOE). The DOE Office of High Energy

Physics sponsors our research on electromechanical properties of candidate superconductors

for particle-accelerator magnets. These materials

include low-temperature superconductors (Nb3Sn

and Nb3Al), as well as high-temperature superconductors (Bi-Sr-Ca-Cu-O and Y-Ba-Cu-O).

The purpose of the database produced from these

measurements is to allow the magnet industry to

design reliable superconducting magnet systems.

MILESTONE: By 2003, perform parametric

studies of axial and transverse stress effect on

the electrical performance of second-generation

high-temperature superconductors.

Some of our research is sponsored in part by the

DOE Office of Energy Efficiency and Renewable

Energy. Here, we focus on high-temperature

superconductors for power applications, including transformers, power-conditioning systems,

motors and generators, superconducting magnetic

energy storage, and transmission lines. In all

these applications, the electromechanical properties of these inherently brittle materials play an

important role in determining their successful

utilization.

MILESTONE: By 2002, create the first data base of

mechanical properties of coated superconductor

substrates at cryogenic temperatures.

In the area of low-temperature superconductors,

we have embarked on a fundamental program to

generalize the Strain Scaling Law (SSL), a magnet design relationship we discovered more than

a decade ago. Since then, the SSL has been used

in the structural design of most large magnets

based on superconductors with the A-15 crystal

structure. However, this relationship is a onedimensional law, whereas magnet design is threedimensional. Current practice is to generalize the

SSL by assuming that distortional strain, rather

than hydrostatic strain, dominates the effect.

Recent measurements in our laboratory suggest

that this assumption is invalid. We are now

developing a measurement system for carefully

determining the three-dimensional strain effects

in A-15 superconductors. The potential financial

consequences of these measurements for very

large accelerator magnets are considerable.

MILESTONE: By 2003, develop the

measurement techniques and obtain the data

needed to generalize the Strain Scaling Law from

one to three dimensions.

Critical current-field-strain surface for the A-15

superconductor Nb3Sn at 4 kelvins.

Accomplishments

! Measurements of Transverse Stress on

Coated High Temperature Superconductors —

We completed the first measurements of transverse stress effects in second-generation high

temperature superconductors, Y-Ba-Cu-Ocoated, rolling-assisted, biaxially-textured substrates (RABiTS) and ion-beam-assisted deposition (IBAD) tapes. The critical current of these

materials is over 1 000 000 amperes per square

centimeter at 77 kelvins, making possible magnet

and power transmission-line applications at

liquid-nitrogen temperature. Our measurements

program is the only one looking at the electromechanical performance of these new materials.

Before these measurements, the available electromechanical data on these conductors were

limited to a few measurements of bending strain

versus critical current. The electromechanical

performance of the RABiTS conductor, which

consists of brittle superconductor and buffer

layers deposited on a substrate of soft, pure Ni,

was particularly suspect. The results showed that

the ion-beam-textured material behaves well

under stress, but the deformation-textured conThe NIST-Boulder labs

have several

specialized and

unique systems for

measuring the effects

of mechanical stress

and strain on

superconductor

performance. NIST

enabled ASC to

demonstrate that our

Bi-2223 conductor has

a transverse

compressive stress

tolerance greater than

100 megapascals.

Dr. L. J. Masur

Senior Manager

American Superconductor Corporation
 26 Electronics and Electrical Engineering Laboratory

ductor, which is currently made using pure Ni,

may have to be constructed from stronger Ni

alloys to withstand the magnetic stress encountered in commercial magnet applications. Our

data are being sought both to guide government

funding decisions for new conductor development, as well as to provide feedback to industry

on the technical development of these new conductor materials.

Comparison of the effect of transverse stress (in

megapascals) on the critical-current density Jc of

various high-temperature tape superconductors:

Y-Ba-Cu-O on an Inconel IBAD substrate, Y-BaCu-O on a pure Ni RABiTS, Bi2Sr2Ca2Cu3Ox with Ag

and oxide dispersion strengthened Ag matrices,

and Bi2Sr2Ca1Cu2Ox with oxide-dispersionstrengthened Ag matrix and double sheathed

with Ag and Ag-Al matrices.

The timing is particularly important for the

upgrading of electric power service to urban

areas, as well as for new magnet technology

being developed for stabilizing electric power

grids operating at high capacity levels. Using our

recently developed fatigue testing facility, we

also made the first high-cycle fatigue measurements on Bi2Sr2Ca2Cu3Ox superconductors. The

initial results indicate there may be significant

accumulated damage on mechanically cycling

these materials, such as they would experience in

repeatedly charged electromagnets.

! New Class of Superconductors Shown to

Tolerate Stress — Our measurements on a new

class of flexible high-temperature coated superconductors have shown that the use of frictional

support from a high-yield structural material cowound with the superconductor can greatly

improve their transverse stress tolerance. This

should allow these new superconductors to be

used in high-field magnet applications. The

effects of static and cyclic transverse stress on the

critical current of Y-Ba-Cu-O coated tapes of

textured Ni were carried out at 76 kelvins. When

subjected to monotonic loading, critical current

degraded by about 1 percent. However, when

samples were tested with frictional support removed between each measurement, critical

current degraded by 7 percent to 26 percent.

Microstructural data also show that improvement

in stress tolerance may be achieved by providing

lateral transverse support to the superconductors

in magnet applications.

Scanning electron micrograph of the Y-Ba-Cu-O

on an Inconel IBAD substrate after static and

cyclic transverse stress testing to 122 megapascals, showing the pattern of longitudinal cracks

along the length of the tape near the tape edge.

Scanning electron microscopy of ion-beamtextured tapes subjected to transverse stress show

a series of thin longitudinal cracks (along the

direction of the transport current) near the tape

edges; the center of the tape, however, was free

of any observable cracks. This indicates that the

failure is due to in-plane transverse tensile strain.

! Stress Effects on Nb3Sn Produced by

Chemical-Vapor Deposition — As part of an

investigation of three-dimensional stress effects

in Nb3Sn superconductors, the effect of transverse stress was measured in several specimens

of a Nb3Sn tape produced using a chemical-vapor

deposition process. This conductor was selected

for its relatively simple structural geometry,

which lends itself to mechanical modeling. Previous measurements of numerous other Nb3Sn

conductors have shown large degradation of

critical-current density (about 40 percent) with

transverse stress; however, the degradation of this

conductor was less than 1 percent at 170

megapascals. Understanding this unexpected and

seemingly remarkable behavior will be an important step in extending the existing Strain

Scaling Law from two to three dimensions.

! New Monograph on Contact Techniques —

We completed a monograph on contact techniques for high-temperature superconductors.

The information is particularly relevant for criti-
 Magnetics Group 27

cal-current measurements of the new coated

superconductors, where films carrying 500 amperes of current are now being fabricated. The

higher currents have resulted in severe contact

heating problems in critical-current tests, usually

resulting in vaporization of the samples. This

chapter details techniques for reducing the contact resistivity of such contacts by up to two

orders of magnitude. Many requests were received for this chapter at a recent Department of

Energy peer review on superconductor development for electric-power utilities.

Recent Publications

J. W. Ekin, “Superconductor Measurement Techniques and

Cryostat Design,” in Applications of Superconductivity, H.

Weinstock, ed., Kluwer Academic Publishers, Dordrecht, pp.

641-658 (2000).

S. E. Bray, J. W. Ekin, C. Clickner, and L. Masur, “Transverse Compressive Stress Effects on the Critical Current of

Bi-2223/Ag Tapes Reinforced with Pure Ag and OxideDispersion-Strengthened Ag,” J. Appl. Phys. 88, 1178-1180

(July 2000).

Y. Xu and J. W. Ekin, “Tunneling Characteristics and LowFrequency Noise of High-TC Superconductor/Noble-Metal

Junctions,” Proc. 17th Symp. Energy Eng. Sci., U.S. Dept. of

Energy, CONF-990001, 17-25 (November 1999).

P. E. Kirkpatrick, J. W. Ekin, and S. L. Bray, “A Flexible

High-Current Lead for Use in High-Magnetic-Field Cryogenic Environments,” Rev. Sci. Instrum. 70, 3338-3340

(August 1999).

Y. Xu, J. W. Ekin, and C. C. Clickner, “Low-Frequency

Noise of YBCO/Au Junctions,” IEEE Trans. Appl. Supercond. 9, 3990-3993 (June 1999).

Y. Xu, J. W. Ekin, C. C. Clickner, and R. L. Fiske, “Oxygen

Annealing of YBCO/Gold Thin-film Contacts,” Adv. Cryo.

Eng. (Materials) 44, 381-387 (December 1998).
 28 Electronics and Electrical Engineering Laboratory

Appendix A:

Laboratory Facilities

Italics indicate that apparatus is unique or one of only a few in the world.

Materials Preparation and Film Deposition

! Computer-controlled, ultrahigh-vacuum deposition system

! Computer-controlled, ultrahigh-vacuum, multi-target sputtering system with in-situ

measurement of magnetoresistance and scanning tunneling microscope

! Ultrahigh-vacuum surface analysis system

! Laser-ablation system

! Electron-beam deposition system

! Electron-beam lithography

! Optical lithography

! Furnaces for preparation of micro-electromechanical systems, including boron diffusion

doping, wet and dry oxidation, and low-pressure chemical-vapor deposition of polysilicon,

silicon nitride, and low-temperature oxide

! Furnaces for reacting superconductors

Structural Characterization

! High-resolution x-ray diffractometer

! Scanning-electron microscope

! Atomic-force microscope

Characterization of Magnetic Materials

! Vibrating-sample magnetometer

! AC susceptometer

! SQUID magnetometer

! Alternating-gradient force magnetometer

! Induction-field looper

! Magneto-optic Kerr effect magnetometer

! Time-resolved second-harmonic magneto-optic Kerr effect system

! Wide-field magneto-optic microscope

! Microwave pulsed-magnetic-field sources

! Pulsed inductive microwave magnetometer

! Magnetic-force microscope

! Magnetic-resonance force microscope

! Ferromagnetic-resonance probe microscope

! Micro-resonating torque magnetometer

Characterization of Magnetic Devices

! Local magnetoresistance scanning-probe station

! Time-resolved magnetoresistance of magnetic random-access memory devices

! Variable-temperature microwave probe station

! Industry-standard spin stand

! Scanning magnetoresistance probe for forensic analysis of recording media
 Magnetics Group 29

Characterization of Superconductors

! Large-bore superconducting magnets up to 18 teslas

! Measurement of critical current up to 2500 amperes

! Low-resistance (1 nano-ohm) measurements of stabilizer materials

! Simulation of transport properties at room temperature

! Low-noise, 1000 ampere dc power supply with current ramp rates up to 10 000 amperes

per second

! High-field electromechanical measurement apparatus (axial, transverse, and hoop stress)

! Measurement of electrical transport and noise in superconductor interfaces

! Magnetic measurement of ac losses in superconductors
30 Electronics and Electrical Engineering Laboratory

Appendix B:

Postdoctoral Research Associateships

NIST offers postdoctoral research associateships in collaboration with the National Research

Council (NRC). Research topics and associated advisors for the EEEL Magnetics Group are

listed below. Complete information and applications forms for all NIST NRC postdoctoral

offerings are available at http://www.nas.edu/rap/ (click on “RAP SEARCH”). Contact a prospective advisor to discuss details of proposed work and the application process. If you do

not find a topic that exactly matches your interest, please contact an advisor in a similar

discipline. U.S. citizenship is required for NIST postdoctoral appointments.

Fabrication and Properties of High-Tc Superconducting Films and

Interfaces

Contact: Jack Ekin, 303-497-5448

Research is conducted on the electromagnetic and transport properties of high-Tc superconductor thin

films and multilayer structures in the Y-, Bi-, and T1-based material systems. Particular emphasis is

given to understanding and controlling interfaces for junction applications, as well as developing

methods for making reliable electrical connections to the oxide superconductors. Our work also focuses on modeling and understanding the transport and noise characteristics of oxide/normal-metal

interfaces.

High-Tc Superconducting Measurements and Materials

Contact: Jack Ekin, 303-497-5448

We study the electrical and mechanical properties of high-Tc superconducting materials including the

effects of stress on transport properties, weak-link effects, and anisotropy limitations on superconduction properties. Short-sample conductors are tested and their mechanical, magnetic field, and electrical

limits are modeled and correlated with tests on composite magnet coils.

Low-Tc Superconductor Measurements

Contact: Jack Ekin, 303-497-5448

An interdisciplinary study of the physical, mechanical, and electrical properties of superconducting

materials and composites is being conducted. Experimental programs include the effect of stress and

fatigue on superconducting critical parameters, electrical and/or metallurgical studies of the problems

of superconductor stabilization, and characterization studies of new superconducting materials. Theoretical studies concentrate on flux pinning and the intrinsic effect of strain on the superconducting

state.
 Magnetics Group 31

Superconductor Measurements

Contact: Loren Goodrich, 303-497-3143

We develop and evaluate measurement techniques to determine the critical parameters and matrix

properties of superconductors. We study conventional superconductors, Nb-Ti and Nb3Sn, and the

newer high-transition-temperature materials. We conduct fundamental studies of the superconductingnormal transitions and parameters that affect their accurate determination such as current transfer,

strain, or inhomogeneities in materials and fields. We develop theoretical models to interpret current

redistribution and component interactions in composite superconductors.

Magnetic Measurements for the Data Storage Industry

Contact: Ron Goldfarb, 303-497-3650

We invite proposals for the development of new, quantitative, metrological techniques to characterize

the magnetic properties of small magnetic structures. Examples of such structures include recording

and giant-magnetoresistive read heads at various stages of production, patterned recording media, and

magnetic random-access memory elements. Ideally, the measurement methods would be transferable

to industry for use in quality control and production.

Magnetostriction Measurements in Thin Film

Contact: Ron Goldfarb, 303-497-3650

Magnetostriction refers to the dimensional change in a ferromagnetic material when it is magnetized in

an applied field. We are interested in developing tools to measure magnetostriction (and inverse magnetostriction) in thin films and multilayers of high permeability magnetic alloys used in recording

heads. Applicants should have an interest in magnetic metrology and the data-storage industry. Available characterization tools include vibrating-sample, alternating-gradient, and SQUID magnetometers;

x-ray diffraction; and atomic-force, magnetic-force, and electron microscopes. Thin-film deposition

chambers and a fully equipped cleanroom are also available.

Properties of Nanometric Magnetic Particles and Ultrathin Films

Contact: Ron Goldfarb, 303-497-3650

This project develops magnetic measurement techniques and phenomenological models for the characterization of magnetic particles, molecules, and thin films on the order of 1-10 nm. Research proposals are invited to measure and understand such materials for use in the areas of ultrahigh-density recording media, biomagnetism, medical therapeutics, microwave absorbers, radio-frequency transformers, magnetic inks, and extruded permanent magnets. Collaborations are encouraged.

Atomic-Scale Information Storage

Contact: John Moreland, 303-497-3641

We are investigating novel techniques capable of ultrahigh-density information storage at atomic

scales. Devices that rely on magnetic, electrostatic, morphological, or other variations in storage media

approaching atomic scales are considered in response to a recognized need to shift information storage

paradigms in the 21st century. Scanned probe microscopy is being used to write atomic scale “bits”

and to study the properties and fundamental recording processes in different kinds of storage media.

Magnetic Resonance Force Microscopy

Contact: John Moreland, 303-497-3641

Magnetic-resonance force microscopy (MRFM) is a promising imaging technique based on the magnetic coupling between magnetic spins and an ultra-sensitive micro-cantilever. In principle, MRFM

should have elemental identification capabilities with sub-angstrom spatial resolution in three dimensions representing a tremendous advancement in the field of magnetic resonance imaging (MRI).

Several technical issues must be addressed before an atomic-scale apparatus of this kind can work: (1)

fabrication of high-sensitivity cantilevers, (2) development of computer-based MRI imaging schemes

for a scanning probe, and (3) construction of an ultra-sensitive AFM readily adaptable to cryogenic

high-field operation.
32 Electronics and Electrical Engineering Laboratory

Micro-Electromechanical Systems for Metrology

Contact: John Moreland, 303-497-3641

We are developing micro-electromechanical systems (MEMS) with integrated components for precision measurement purposes. Work focuses on the following goals: (1) improving the performance of

fundamental standards instrumentation by developing novel detectors and more fully integrated measurement systems, (2) exploring the impact of MEMS and MEMS-based metrology on the future development of the microelectronics and data storage industries, and (3) improving the manufacturing yield

with MEMS probe assemblies designed for production line testing. Our clean room facility is equipped

for bulk micromachining of silicon and LPCVD of polysilicon and silicon nitride films on sacrificial

glass layers. We are interested in all aspects of research, including the design and fabrication of novel

MEMS structures, as well as the testing and integration of MEMS structures into precision measurement instruments.

Nanoscale Imaging for Magnetic Technology

Contact: John Moreland, 303-497-3641

The magnetic storage industry has advanced to the stage where nanometer-scale morphological and

physical properties play an important role in current and future disk drive performance. In its many

forms, scanned probe microscopy (SPM) can be used to measure roughness, device dimensions, electromagnetic field patterns, and various physical processes at nanometer scales, which provides important information about the fundamental operation and limitations of drive components. Our goal is to

help tailor SPM techniques for these applications. We are investigating scanning tunneling microscopy, atomic-force microscopy, magnetic-force microscopy, scanning potentiometry, and scanning

thermometry for their usefulness.

Magnetism in Thin Films and Surfaces

Contact: David Pappas, 303-497-3374

Research efforts on magnetic thin films and multilayers have been redoubled as the need for higher

density storage media increases. Opportunities are available to work in a wide range of topics. Areas of

interest include developing measurements such as in-situ SQUID Magnetometry, magneto-optic Kerr

effect (MOKE) susceptibility measurements, and spin-polarized electron spectroscopy. In addition,

there is ongoing work to generate standard samples for magnetic force microscopes with nanoscalepatterned magnetic media, as well as a strong interest to incorporate MOKE and magnetostrictive

devices into micro-electromechanical systems.

Nanoscale Magnetic Structures

Contact: Stephen Russek, 303-497-5097

Ultra-small magnetic structures will be fabricated using e-beam and scanned probe lithographies in a

variety of magnetic thin-film systems. The systems studied will include advanced longitudinal and

perpendicular media, multilayer systems, and single crystal films. The goal of this research will be to

understand the physics of ultra-small magnetic structures and their implications for the limits of magnetic data storage. The switching process will be studied as a function of size, shape, and temperature

to characterize thermally activated and quantum mechanical switching mechanisms. The interaction of

magnetic particles in large arrays will be studied. The magnetic structure will be characterized using

magnetic force microscopy, magnetometry, and transport measurements.

Spin-Dependent Electron Transport in Metals, Conducting Oxides,

and Semiconductors

Contact: Stephen Russek, 303-497-5097

Spin-dependent transport is a widely used, yet poorly understood phenomena. Giant magnetoresistive

(GMR) devices and magnetic tunnel junctions (MTJ) are being developed for use in magnetic recording heads, magnetoresistive random-access memory, and industrial magnetic sensors. The market for

these devices is enormous, in the tens of billions of dollars. The goal of this research is to develop a

better fundamental understanding of spin-dependent transport in magnetic metals, normal metals,
Magnetics Group3

conducting oxides, and semiconductors and their interfaces. Research involves the fabrication of novel

GMR, MTJ, and novel magnetic semiconductor devices using a state-of-the-art 8-source ultrahighvacuum (UHV) deposition system, and a combination of optical, e-beam, and scanned probe lithography. Spin dependent scattering and spin injection effects will be studied in nanoscale devices over a

temperature and frequency range of 4 K to 500 K and dc to 40 GHz. Device level measurements will

be compared with spin-polarized transport measurements using an in-situ UHV scanning tunneling

microscope.

High-Speed Magnetic Phenomena

Contact: Tom Silva, 303-497-7826

Experimental methods to determine fundamental limits to the data rate of magnetic devices are being

developed. Both low- (“soft”) and high-coercivity (“hard”) materials are studied. Experimental techniques include electrically sampled inductive detection and time-resolved magneto-optics for the study

of soft magnetic materials. Quantitative Kerr microscopy is used for the measurement of switching

speed in hard magnetic materials. Extensive facilities exist, including a 20-GHz sampling oscilloscope,

a 50-fs mode-locked Ti:sapphire laser, and a digital Kerr microscope with a high-performance chilled

CCD camera. Commercial and experimental solid-state instrumentation is used for the generation of

microwave pulses. Waveguide technology is employed to deliver subnanosecond magnetic field pulses

to samples. Waveguide structures are lithographically fabricated on site in a state-of-the-art cleanroom,

which includes mask generation facilities. Applications are encouraged from those who have a strong

experimental background in magnetism, especially in high-frequency magnetic phenomena such as

ferromagnetic resonance.

Nonlinear Magneto-Optics

Contact: Tom Silva, 303-497-7826

The second harmonic magneto-optic Kerr effect (SHMOKE) is under investigation as a tool for the

study of interfacial magnetism. SHMOKE shows strong sensitivity to the magnetization at optically

accessible interfaces between ferromagnetic and non-ferromagnetic films, yet SHMOKE does not

require exotic facilities, such as ultrahigh vacuum (UHV) or synchrotron radiation. Therefore,

SHMOKE shows great promise as an industrial diagnostic instrument for the optimization of giant

magnetoresistive sensors and magnetic tunnel junctions, where interfacial magnetism strongly influences device performance. SHMOKE also exhibits a strong magneto-optic signal, with the magnetic

contrast approaching 60% in some sample systems. Extensive resources for the study of SHMOKE

exist, including a mode-locked 50-fs Ti:sapphire laser, coincident-photon detection electronics, photoelastic modulators, lock-in amplifiers, and sample translation stages. Samples may be produced on site

with a state-of-the-art 8-source UHV sputtering system. Applicants are preferred with a strong experimental background in magnetic thin films, magnetic multilayers, magneto-optics, and/or nonlinear

optics.

Thermal Instability of Magnetic Thin Films

Contact: Tom Silva, 303-497-7826

As the grain size of thin-film magnetic recording media steadily decreases with increasing areal capacities, we are concerned that recorded information may be erased as a result of thermally activated

switching of the individual grains — the so-called “superparamagnetic limit.” Our goal is to understand the fundamental mechanisms, which result in thermal erasure through the measurement of various phenomena, including magnetic viscosity and the time dependence of coercivity. Emphasis is

placed on determining the thermal stability of media over a wide range of time scales, from those

accessible with large-scale magnetometers to those that use pulsed microwave fields. The final goal is

a measurement technique for the determination of data stability in media without resorting to meantime-before-failure analysis. Extensive facilities exist, including numerous magnetometers (vibratingsample magnetometer, alternating-gradient magnetometer, SQUID magnetometer), a transmission

electron microscope for the determination of grain size, and a state-of-the-art 8-source ultrahigh vacuum sputtering system for the preparation of samples. Applicants with a strong experimental background in magnetism — especially magnetic thin-film preparation and characterization — are encouraged to apply.

33
34 Electronics and Electrical Engineering Laboratory

Appendix C:

EEEL Magnetics Group Staff

Alan Cookson, EEEL Acting Deputy Director, 301-975-2220, alan.cookson@nist.gov

Fred Fickett, Acting Division Chief for Boulder, 303-497-3785, fickett@boulder.nist.gov

Ron Goldfarb, Acting Group Leader, 303-497-3650, goldfarb@boulder.nist.gov

Linda Derr, Administrative Officer, 303-497-4202, derr@boulder.nist.gov

Ruth Corwin, Secretary, 303-497-5477, corwin@boulder.nist.gov

Magnetic Recording Measurements

David Pappas, Project Leader, 303-497-3374, pappas@boulder.nist.gov

Steve Arnold, Contractor, 303-497-3381, arnoldcs@boulder.nist.gov

Gideon Shalev, PREP Student, 303-497-4283, shalev@boulder.nist.gov

(Also contributing in FY 2000: Carla Eunice, David Stevenson)

Magnetodynamics

Tom Silva, Project Leader, 303-497-7826, silva@boulder.nist.gov

Tony Kos, 303-497-5333, kos@boulder.nist.gov

Matt Pufall, Postdoctoral Associate, 303-497-5206, pufall@boulder.nist.gov

Fabio da Silva, Guest Research Scientist, 303-497-3873, fcss@boulder.nist.gov

(Also contributing in FY 2000: Pavel Kabos, Kevin Pettit, Nick Rizzo, Gordon Yee)

Nanoprobe Imaging

John Moreland, Project Leader, 303-497-3641, moreland@boulder.nist.gov

(Also contributing in FY 2000: Albrecht Jander, Peter Johnson)

Magnetic Thin Films and Devices

Stephen Russek, Project Leader, 303-497-5097, russek@boulder.nist.gov

Bill Bailey, Postdoctoral Associate, 303-497-3701, baileyw@boulder.nist.gov

Shehzaad Kaka, PREP Graduate Student, 303-497-7365, kaka@boulder.nist.gov

Fred Mancoff, Postdoctoral Associate, 303-497-4987, mancoff@boulder.nist.gov

Bill Rippard, Postdoctoral Associate, 303-497-3882, rippard@boulder.nist.gov

(Also contributing in FY 2000: Terry Gafron)

Standards for Superconductor Characterization

Loren Goodrich, Project Leader, 303-497-3143, goodrich@boulder.nist.gov

Ted Stauffer, 303-497-3777, stauffer@boulder.nist.gov

Superconductor Electromagnetic Measurements

Jack Ekin, Project Leader, 303-497-5448, ekin@boulder.nist.gov

Najib Cheggour, Guest Research Scientist, 303-497-3815, cheggour@boulder.nist.gov

Cam Clickner, 303-497-5441, clickner@boulder.nist.gov

(Also contributing in FY 2000: Steve Bray, Tim Collins, Roland Sesselmann, Yizi Xu)

— December 1, 2000
 Magnetics Group 35

Appendix D:

Prefixes for the

International System of Units (SI)

Multiplication

Factor

Prefix Symbol Multiplication

Factor

Prefix Symbol

1024 yotta Y 10−1 deci d

1021 zetta Z 10−2 centi c

1018 exa E 10−3 milli m

1015 peta P 10−6 micro μ

1012 tera T 10−9 nano n

109 giga G 10−12 pico p

106 mega M 10−15 femto f

103 kilo k 10−18 atto a

102 hecto h 10−21 zepto z

101 deka da 10−24 yocto y
 36 Electronics and Electrical Engineering Laboratory

Appendix E:

Units for Magnetic Properties

Symbol Quantity Conversion from Gaussian and cgs emu to SI

Φ magnetic flux 1 Mx → 10−8

 Wb = 10−8 V·s

B magnetic flux density,

magnetic induction

1 G → 10−4 T = 10−4 Wb/m2

H magnetic field strength 1 Oe → 103/(4π) A/m

m magnetic moment 1 erg/G = 1 emu → 10−3 A·m2 = 10−3 J/T

M magnetization 1 erg/(G·cm3) = 1 emu/cm3

→ 103

 A/m

4πM magnetization 1 G → 103

/(4π) A/m

σ mass magnetization,

specific magnetization

1 erg/(G·g) = 1 emu/g → 1 A·m2

/kg

j magnetic dipole moment 1 erg/G = 1 emu → 4π × 10−10 Wb·m

J magnetic polarization 1 erg/(G·cm3) = 1 emu/cm3

→ 4π × 10−4

 T

χ, κ susceptibility 1 → 4π

χρ mass susceptibility 1 cm3

/g → 4π × 10−3 m3/kg

μ permeability 1 → 4π × 10−7

 H/m = 4π × 10−7 Wb/(A·m)

μr relative permeability μ → μr

w, W energy density 1 erg/cm3

→ 10−1

 J/m3

N, D demagnetizing factor 1 → 1/(4π)

Gaussian units are the same as cgs emu for magnetostatics; Mx = maxwell, G = gauss,

Oe = oersted; Wb = weber, V = volt, s = second, T = tesla, m = meter, A = ampere,

J = joule, kg = kilogram, H = henry.
January 2001

For additional information contact:

Telephone: (303) 497-5477

Facsimile: (303) 497-5316

On the Web: http://www.eeel.nist.gov/magnetics