American Institute of Physics (AIP)
Journal of Applied Physics
57 (1985), S. 3831-3831
AIP Digital Archive
Magnetoresistance detectors are used to observe the magnetic state of microscopic parts of magnetized samples. The planar Hall effect can be used instead. Both effects can be applied to find out the logic "1'' or "0'' state of magnetic storage devices. They also can be used for a quantitative and sensitive measurement of magnetic fields as well as a magneto-elastic strain gauge. Soft magnetic permalloy films are appropriate for the field detection while amorphous Fe1−xBx films are suitable for the strain measurements. The sensor films have to show a uniaxial anisotropy. The strength of it determines the range of the detectable fields and strains. The sensitivity of the magnetoresistance emr=dΔU/dH=2( ρ⊥−ρ(parallel)) 1/db JH/HK2(V/Oe) depends linearly on the magnetic field H applied along the hard axis. l, d, b are the film length, thickness and width, respectively. The sensitivity of the planar Hall effect, which is given by epl=dUpl/dH =( ρ(parallel)−ρ⊥)s/db J(1/HK) is independent of the applied field along the hard axis as long as H(very-much-less-than)HK. s is the separation of the Hall contacts. Both sensitivities are reciprocal to the uniaxial anisotropy, HK as long as the applied field, H is smaller than HK. The theoretically expected sensitivity usually is decreased by domain splitting and the influence of the magnetization ripple. The smaller HK is (the larger the sensitivity is) the stronger is the influence of the ripple. It gives an upper limit of the interval in which external fields or applied strains can be quantitatively measured. Double layered films can prevent the domain splitting. The sensor theory including the ripple and experimental data will be given.
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