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Nanoscale Magnetic Sensors
NIST Competence Program

Current Uses of Magnetic Sensors

Compass for tactical unmanned aerial vehicles, Geophysical exploration, Non-destructive testing – bridges, Health care Non-invasive medical evaluation, and Data Storage (Magnetic RAM and Hard disk drive heads)

FBI Magnetic Media Forensic Audio Examinations

Types of media submitted include:
Cassette & digital audio tapes (answering machine and hand-held), video tapes, flight recorders, M.O. discs

Types of Cases Submitted:
Terrorism, homicide, armed robbery, financial, health care fraud, police corruption, money laundering, drugs, skyjacking

Apply scanning MR microscopy to tape
Commercial HGA with MR (AMR, GMR, TMR) reader polished slider on low force suspension

Use standard AC coupling to MR development.
Problems include Thermal “popcorn” from tape roughness, and lose DC signatures and head edge marks

High Resolution Computer Rendering

Detects zero frequency signals, higher contrast (45 – 50 dB), field direction (polarity), higher resolution

NIST program to develop low-noise sensors
Nano-magnetic engineering includes Anisotropy dispersion, the Effects of shape and defects, and Magnetic fluctuations




Magnetic Configuration of zig-zag thin films

Magnetism in zigzag shaped thin film elements is investigated using scanning electron microscopy with polarization analysis, magneto-transport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length of the element, and is strongly correlated to the corrugated edges. We show that this simple and unique geometry can be used as a natural means of biasing the magnetization relative to the current to form a magnetic field sensor. In this configuration the sensors are primarily sensitive to fields parallel to the applied current. These results can be interpreted in terms of a coherent rotation model of the magnetization. These devices are scalable to nanoscale dimensions.Magnetism in zigzag shaped thin film elements is investigated using scanning electron microscopy with polarization analysis, magneto-transport measurements, and micromagnetic simulations. We find that the angle of magnetization alternates along the length of the element, and is strongly correlated to the corrugated edges. We show that this simple and unique geometry can be used as a natural means of biasing the magnetization relative to the current to form a magnetic field sensor. In this configuration the sensors are primarily sensitive to fields parallel to the applied current. These results can be interpreted in terms of a coherent rotation model of the magnetization. These devices are scalable to nanoscale dimensions.

Scanning Electron Microscopy (SEM) shows topography

Scanning Electron Microscopy with Polarization Analysis (SEMPA) shows magnetization

But as you change expand width from previous figure:

Conclusions:
There are many current and new applications for MR sensors. Clearly, there is still a lot of room at the bottom for nano- engineering magnetic sensors. In the particular case of a single layer MR sensor with a zigzag shape, the geometrical biasing mechanism works over a wide range of size scales, from the nanoscale region (width 250 nm), where it was originally reported, to the microscale (width 5 ¹m), where this study was conducted. This scaling should extend to small sizes until the distance between corners becomes comparable to the domain wall width in the magnetic material. We also find that modern computational models, such as OOMMF, can be used to understand and accurately predict the magnetic properties of devices at the nanoscale level. Based on the scalability and the fact that these elements can be described with a simple coherent rotation model, we expect this type of nano-engineering of the shape of the magnetic layer will have a significant impact in the areas of magnetic field sensors and memory applications.

This page was based on the powerpoint presentation by David Pappas entitled "The lost 18 ½ minutes of Nixon’s presidency: A study of residual magnetic structure in erased magnetic media using magneto-resistive microscopy" which can be viewed here.

More information on zig-zag magnetics sensors can be found in "Zigzag shaped magnetic sensors."

Nanoscale engineered sensors links you to the original presentation and provided the basis for this focus.

Click on the Magnetic Sensor Workshop link for the November 7, 2003 conference for the information roadmap.