# Presentation: 699833

## “The lost 18 1⁄2 minutes of Nixon’s presidency: A study of residual magnetic structure in erased magnetic media using magneto-resistive microscopy

*National Institute of Standards and Technology*
- Boulder, CO

- “The lost 18 1⁄2 minutes of Nixon’s presidency: A study of residual magnetic structure in erased magnetic media using magneto-resistive microscopy

## Ongoing projects

**Quantum Computing**
- NIST - Dustin Hite, John Martinis, Ray Simmonds, Rob McDermott, Ken Cooper, Matthias Stefan
- Colorado College - Kristine Lang
**Surface & 2-dimensional Magnetism**
- NIST - Dustin Hite, Stephen Arnold, Sheongshik Oh
**Magneto-resistive microscopy**
- NIST - F. daSilva, W. Uhlig, J. Unguris, S. Russek, W. Egelhoff, W. Rippard
- Seagate - Alexey Nazarov
- FBI Audio Forensics Laboratory - Ken Marr
- National Security Agency -  Dave Krefft
- Intel Corporation - Travis Eiles

## Magneto-resistive microscopy

- Applications of magnetic sensors
- Requirements in forensics
- Images Homeland security
- Non-destructive evaluation
- Sensor development
- Programs at NIST
- Novel sensor designs

## Current uses of magnetic sensors 

-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

- Current uses of magnetic sensors

## Current uses of magnetic sensors 

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Current uses of magnetic sensors 

- Current uses of magnetic sensors

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Current uses of magnetic sensors 

- Current uses of magnetic sensors

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Current uses of magnetic sensors 

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Current uses of magnetic sensors 

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Current uses of magnetic sensors 

-  Compass for tactical unmanned aerial vehicles
-  Geophysical exploration
-  Non-destructive testing – bridges
-  Health care     Non-invasive medical evaluation
- 	Magnetic liver & lung “biopsies”
- 	Magneto-cardiography (MCG)
- 	Magneto-encephalography (MEG)
- Data Storage
-  Magnetic RAM
-  Hard disk drive heads

## Intense development of magnetic sensors has enabled high density hard disk drive storage

**1985**

**1990**

**1995**

**2000**

**2005**

**Typical****Disk**
**Capacity****in Gigabytes**

**0.01**

**0.1**

**1**

**10**

**100**

**Hard Disk Drive Growth Rate**

**30% per year**

**60% per year**

**100%per year**

- Inductive
- read heads

- AMR heads

- GMR heads

- TMR heads

-  Hard drive heads make great scanned probe microscope sensors

-  Specialized sensors  - 	high frequency
- 			shielded
- 			nano-scale devices

- Intense development of magnetic sensors has enabled high density hard disk drive storage

## Use MR head to image magnetic patterns on sample by sliding slowly across surface with micrometers“Static Tester”

- Use MR head to image magnetic patterns on sample by sliding slowly across surface with micrometers“Static Tester”

-  Scan MR head while in direct             	contact with disk
-  Use both the read & write elements
-  AC coupled to reject low frequency 	thermal effects
- _Applications_
-   Calibrate R/W fields/currents
-  Thermal decay of data
-   Frequency response of heads
-   Spatial transfer function

- I

- V

- R

## Can scan in hdd data with piezo’s

Time consuming, need to patch images together

Leave data recovery for spin stand imaging

- Time consuming, need to patch images together
- Leave data recovery for spin stand imaging

- Low level digital computer data written & imaged with scanning head

- Platter from 1 GB hdd
- circa 1996

- 100 m

## FBI - magnetic mediaforensic audio examinations

-    _Types of cases submitted_
-  Terrorism
-   Homicide
-   Armed Robbery
-   Financial, Health Care Fraud
-   Police Corruption
-   Money Laundering, Drugs
-   Skyjacking

**FBI - magnetic media****forensic audio examinations**

-    _Types of media submitted_
-  Cassette & digital audio tapes
-  Answering machine
-  Hand-held
-  Video tapes
-  Flight recorders
-  M.O. discs

## 674 audio analysis cases in  20023 investigators

-  Authenticity & signal analysis requires low-level magnetic imaging
-  Very time consuming
-  High profile cases
-  Need to testify in court

## Audio tape authenticity evaluation

-           ferrofluid  +  microscope  +  dexterity + patience
- => Authenticity analysis - erasure, alteration, duplication
-  Need to screen entire reels of tape
-  Need to identify signatures of evidence tampering – head edge marks

- Write head

- Erase head

- tape

- Ferro-fluid image
- of test tape

- 4 mm

## Ferro-fluid magnetic imaging 

- Magnetic particles  assembled on flux lines  - “Bitter method”
- Good resolution for analog media
- Very fine particles contaminate evidence – especially   digital
- Low dynamic range (20 dB) – black & white image
- Don’t get direction of B – Can’t rebuild the waveform

- Ferro-fluid magnetic imaging

- side view

- B

- recorded waveform

## Other magnetic imaging techniques

- Magnetic force microscopy (MFM)
- High resolution, polarity sensitive
- Cost, mechanical range ~ 0.1 mm, slow
- Scanning SQUID microscopy
- Polarity sensitive, long range
- Cryogens, low resolution, cost
- Magneto-optically active garnet crystals
- High resolution, fast, polarity sensitive
- Applied field necessary, complicated optical setup, expensive
- Magneto-resistive elements
- High resolution, contrast, polarity, fast, long scans, inexpensive,                	**scalable**
- Thermal asperities and drift

## Apply scanning MR microscopy to tape

- Commercial HGA with MR (AMR, GMR, TMR) reader
-  	polished slider on low force suspension
- 	=> hard disk drive OEM parts
- Use standard AC coupling to MR element

- 4 mm

- Problems:
- Thermal “popcorn” from 	tape roughness
-  Lose DC signatures
- 	head edge marks

## Thermal noise rejection and extraction of DC magnetic field from AMR reader

- Modulate current bias, I, on soft adjacent layer
- 	=> Changes the bias angle,  cos2( 1 – (kI + k’Bsig)2

- (ohmic)

- (thermal)

- (MR)

- R

- B,

- Bsignal

## Second harmonic detection

- Bsignal

- Bbias

- 1st harmonic
- (signal +thermal)

- 2nd harmonic
- (signal)

- higher
- harmonics

- (Shelledy, ’74)

- Rejects thermal asperities and modulates the signal for lockin detection

## Scanning 2nd harmonic MR microscope image

- Detect zero frequency signals
- Higher contrast (45 – 50 dB)
- Field direction (polarity)
- High resolution

## High resolution computer rendering

- Write head
- stop event

- Audio test tones

## Other magnetic media

- Video tape
- 871 cases
- Helical scan
- sample 1 m

- Digital Audio tape – need non-invasive technique
- sample 0.1 m
- track pitch 13.6 m

## Analog waveform recovery

- Test sample with a recording of “F B I” in analog audio

-  2 m wide sample
-  Sample every 6 m
- 4 kHz bandwidth
- Voice can be identified

- ~1⁄2 second of data (2.5 cm)

## National Archives and Records Administration Watergate test tape study

- 	from 18 1⁄2 minute gap
-  Record data on Sony - erase with Uher dictaphone
-  Look for evidence of audible speech

- one second

- Did find an edge on the erased audio track
- No recoverable audio on the test tape  

## Digital waveform recovery

- Airline flight data recorder – need to evaluate small scraps of tape
- 8 track
- 0.48 in blocks
- Harvard Bi-phase coding
- Sample every 1 m
- Decoded data blocks with
- 	computer program

- 0

- 10,000

- 20,000

- Distance (m)

- a

- b

- ...000001001110...

## Ongoing sensor array development for real-time imaging

- Requirements:
- Reject thermal asperities
- Low noise
- Scalable for high resolution
- Easily biased & linear
- Measure DC fields
- High yield, robust
- MR imaging arrays
- 64 differential element cassette tape scanner
- Dual barber-pole sensors (128 sensors)
- Developing high density dual stripe arrays
- Need to  understand noise, scalability of sensor, biasing of magnetization

- 4 mm

## NIST program to develop low noise sensors

- Nano-magnetic engineering
- Anisotropy dispersion
- Effects of shape, defects
- Magnetic fluctuations
- Materials development – W. Egelhoff
- Multilayers, amorphous materials
- Device fabrication & applications
- 	S. Russek, D. Pappas, W. Rippard
- Device imaging – J. Unguris, W. Uhlig
- SEMPA
- Device modeling – OOMMF - M. Donahue

## Start with AMR devices – understand noise, shape

- Bias the current at 45o (barber-pole)
- “Barber-pole”
- Single layer
- Not scalable
- Bias magnetization  at 45o with field
- “Dual stripe” and “Soft adjacent layers”
- Scalable
- Multilayer device
- _Bias magnetization with shape?_
- Single layer thin film
- 	Effects of edges - zig-zags
- Scalable Chapman (2003)

- M

- M

- I

- I

- Al

- NiFe

## Magnetic configuration of zig-zag thin films

- Structures defined by optical lithography (scaled up Chapman device)
- Scanning electron microscopy (SEM) shows topography
- SEM with polarization analysis (SEMPA) shows magnetization

- 5 m

- 5 m

- 1⁄4 m

## Remanent from H = 0.15  T

- Explore effect of aspect ratio on remanent magnetization

- Change length

## Change width

- Remanent
- from
- H = 0.15  T

## Quantitative understanding of micro-magnetics

- OOMMF micro magnetic model
- SEMPA magnetization
- image

-  Actual 25o bias
-  Model shows that
-    nano-structure is
-    critical

## Measure magneto-resistance

-  Finite element analysis shows J primarily along axis

- M

- Contacts

## Slide 36

## Slide 37

## Transfer curve of the high aspect ratiozig-zag sensor

- Magnetization rotates as expected
- Sensitive primarily to on-axis fields
- Non-linearity indicates non-ideal biasing

- B

- B

- Scissor mode

- Rotation

## Conclusions

- Many current and new applications for MR sensors
- There’s still a lot of room at the bottom for
- 		nano- engineering magnetic sensors
- Need continued development of sensor technology

## Magnetic field measurement will facilitate NDE of flip-chip integrated circuits

- 2 x 2 cm RAM chip

- Magnetic field
- Mapped over entire chip

- Inversion => current

-  Resolution limited by thickness of wafer, inversion techniques, SNR
- Low field, low -> high frequency applications
-  Arrays will allow better field inversion => lower noise

- Magnetic field measurement will facilitate NDE of flip-chip integrated circuits

## High speed field imaging and inversion using sensor arrays

- Linear scan over features
-    at height z = 1mm

- 2 mm

- I

- 1 mm

- 0.5 mm

- Test structure

- MR sensor array

## Remanent

- From
- H = 0.15 T

## Remanent

- From
- H = 0.15 T