Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1996-10-30
2000-12-26
Patidar, Jay
Electricity: measuring and testing
Magnetic
Magnetometers
360113, G01R 3302, G11B 5127
Patent
active
061665398
ABSTRACT:
The present invention provides a method and apparatus for utilizing magnetoresistance devices for the measurement of weak magnetic fields. An oscillating excitation magnetic field is applied to a magnetoresistive (MR) sensing element such that the MR element is driven into one or both of two antiparallel saturation states. The amplitude of the excitation field is large enough to reverse the magnetization of the soft layer during each cycle. In one embodiment, the MR element is provided with a current, and a voltage proportional to the resistance is measured. Components of the voltage signal at multiples of the excitation frequency are then proportional to the environmental magnetic field. In one embodiment, an MR element having a resistance-versus-field transfer function that is symmetric (e.g., an anisotropic MR element) is used; while in another embodiment, an MR element having a resistance-versus-field transfer function that is asymmetric (e.g., a spin-valve MR element) is used. Various apparatus and methods for measuring the amount of time spent in one or both saturated states versus the unsaturated or transition states are described. In one embodiment, the magnetic excitation field is generated using a current strip deposited onto the top of the other device layers, so that the entire device can be produced on a single chip. In one embodiment, a "flexible" magnetoresistive structure includes a "flexible" ferromagnetic layer having a hard-magnetization-portion layer, and a soft-magnetization-portion layer, thus providing a smooth magnetic transition when this bilayer switches. One embodiment includes a supporting data-read head structure that positions the flexible magnetoresistive (MR) sensing element to sense a magnetic field in a data storage device such as a magnetic-disk drive.
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Dahlberg E. Dan
Moran Timothy J.
Patidar Jay
Regents of the University of Minnesota
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