Dipolar interactions and anisotropic magnetoresistance in metallic granular systems

We revisit the theory of magnetoresistance for a system of nanoscopic magnetic granules in metallic matrix. Using a simple model for the spin dependent perturbation potential of the granules, we solve Boltzmann equation for the spin dependent components of the non equilibrium electronic distribution function. For typical values of the geometric parameters in granular systems, we find a peculiar structure of the distribution function of conduction electrons, which is at variance with the two-current model of conduction in inhomogeneous systems. Our treatment explicitly includes the effects of dipolar correlations yielding a magnetoresistance ratio which contains, in addition to the term proportional to the square of uniform magnetization (), a weak anisotropic contribution depending on the angle between electric and magnetic fields, and arising from the anisotropic character of dipolar interactions.Comment: 9 pages, 2 figures, accepted in PR

Magnetic and Magnetotransport Properties In Co5cu95 Melt-spun Alloys

Giant magnetoresistance (GMR) has been observed in Co5Cu95 alloys fabricated by melt-spinning. The highest MR change of 28.0% occurs for Co5Cu95 after annealing at 450 degrees C for 30 min. Based on the superparamagnetic assumption, the average size of Co particles embedded in Cu matrix, ranging from 3.0 to 6.0 nm, has been determined by simulating the magnetization curves at 295 K which is higher than the blocking temperatures for the samples. Comparison with phenomenological theory for GMR indicates that the interfacial spin-dependent scattering is the dominant scattering mechanism underlying GMR origin in granular systems. Additionally, for the samples in as-quenched state or annealed at temperature T-A=350 degrees C, the electron hybridization and superparamagnetic behaviors of fine Co particles may be responsible for the low value of MR change