Micromagnetic analysis of co-based magnetic nanostructures.

Abstract

Micromagnetic analysis was employed in order predict the dynamical behavior of a variety of magnetic structures utilized in information storage devices. First, the surprising behavior of homogeneous perpendicular recording media was micromagnetically investigated. It is common to model recording media as interacting coherently rotating magnetic moments, but real materials frequently exhibit perpendicular switching fields less than the anisotropy field and a different angular dependence than theoretically expected. Micromagnetic simulations were performed, which included multiple elements per grain and magnetostatic interactions between elements. Two likely explanations have emerged from this analysis: the existence of low anisotropy regions within the first few atomic layers of the sputtered film or anisotropy gradation throughout the grain thickness. Both explanations offer appropriate coercivity reductions; however, grains including anisotropy gradation display this effect at more realistic values of intragranular exchange. Secondly, the lack of inclusion of spin-dependent scattering effects in most micromagnetic studies was addressed in this work. An analytic expression that includes the effect of multiple reflections within the interface of a tri-layer spin-valve composed of materials with partial spin polarization was obtained. Inclusion of this term in a micromagnetic calculation demonstrates the effect of the spin polarization of the magnetic material on the current induced behavior of the structure. We show that neglecting to include interfacial scattering events results in an underestimation of the switching current compared to the method detailed in this thesis. Multiple reflections also produce a strong dependence of the switching current on the magnetocrystalline anisotropy of the fixed layer. This approach was then extended to structures consisting of more than two ferromagnetic layers. Micromagnetic calculations employing this method achieved good agreement with electrical measurements performed on Co/Cu multilayer nanowire arrays.