Determining the AC susceptibility of thin metal films using the anisotropic magnetoresistance

Abstract The differential ac magnetic susceptibility of thin magnetic films was determined using the anisotropic magnetoresistance (AMR) to measure the response of the magnetization to an applied AC magnetic field. The differential AMR was measured with a small AC magnetic field (1 Oe) at frequencies from 5 Hz to 5000 Hz as a function of the magnitude of an applied DC field that was varied from −60 Oe to +60 Oe. A model relating the magnitude of the differential AMR to the differential AC susceptibility was developed. The ferromagnetic films investigated were permalloy, cobalt, nickel, and nickel with an antiferromagnetic nickel oxide layer on one surface. For all the samples investigated, the differential susceptibility magnitude was a function of the DC field magnitude and was frequency dependent, decreasing with increasing frequency.