Modeling Giant Magnetoresistance and Relative Permeability in Granular Films
- PDF / 276,146 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 28 Downloads / 198 Views
MODELING GIANT MAGNETORESISTANCE AND RELATIVE PERMEABILITY INGRANULAR FILMS M.R. PARKER*, J.A. BARNARD**, S. HOSSAIN*, D. SEALE*, M. TAN**, and A. WAKNIS**, The University of Alabama, *Department of Electrical Engineering and "*Department of Metallurgical and Materials Engineering Tuscaloosa, AL 35487-0202 ABSTRACT A model for the field dependence of giant magnetoresistance (GMR) in 'granular' co-sputtered alloy thin films (based on a relatively simple spindependent scattering concept appropriate to superparamagnetic and weakly ferromagnetic films) is applied to new experimental data from the Co90Felo-Ag system. The model and the experimental data can be shown to compare very well with the help of a single adjustable parameter related to spin correlation of adjacent Co-Fe clusters. A careful fit of field-dependent MR data and theory leads to a fairly reliable determination of spin-cluster radius. An analysis of the relative permeability of granular GMR films derived from the generalized form of the Clausius-Mossoti relationship is also presented. For a non-magnetic matrix the effective relative permeability is shown to be materials independent. The permeability model is applied to Co-Au granular films. 1. INTRODUCTION In the last year, remarkably large GMR ratios have been observed[eg.,1-6] in single layer films variously described as 'granular', 'metastable alloys', and 'heterogeneous', but which are generally prepared by co-sputtering a ferromagnet and a nonmagnet which phase separate (cluster) under equilibrium conditions (eg., Co-Cu, Co-Ag). The occurrence of GMR is associated with a microstructure which can be described as consisting of very small ferromagnetic clusters in a $nonmagnetic' matrix. The field dependence of GMR in granular films has been successfully accounted for[7] by extending a simple model of magnetoresistive scattering in granular films due to Gittleman et al[8]. The size of an average spin cluster in the Co-Ag system has been tracked as a function of annealing using this model[7]. The model is outlined below and further refined to allow for assessment of the range of spin cluster sizes present in real films. The relative permeability of granular GMR materials (despite its obvious technological relevance) has not received attention to date. In the second part of this paper a model for the effective relative permeability based on the generalized form of the Clausius-Mossotti relationship is developed. This analysis demonstrates that the effective relative permeability is materials independent and will be determined by geometrical factors alone. 2. FIELD DEPENDENCE OF GMR INGRANULAR MAGNETIC FILMS[7] A simple model of electron scattering due to Gittleman et al[8] is adopted here and reformulated in terms of explicit field dependence. The scattering probability is assumed to be linearly dependent on the degree of correlation of the moments of adjacent pairs of spin clusters averaged over all possible configurations within the film. This is expressed as /m 2, where mi is Mat. Res. Soc. Symp. Pro
Data Loading...
