Transition noise study in oriented longitudinal thin films

Abstract

Microscopic magnetization configurations, related magnetization fluctuations, and transition noise in planar isotropic longitudinal films were studied.[l] As a continuation of that work, here we study the magnetization configurations and transition noise for oriented longitudinal films. In particular, we focus on the distinction between position jitter noise and amplitude noise. The film is modeled as a planar array of hexagonal single domain grains with long range magnetostatic interaction and nearest-neighbor exchange coupling. Magnetization orientations are determined by following the Landau-Lifshitz equations of motion with large damping.[2] The medium magnetic parameters used here are for CO based alloy films and the crystalline anisotropy is uniaxial. The orientations of the easy axes are randomly and uniformly distributed within a solid angle ( with half-cone angle 9 ) about the orientation direction. The study is carried out for e values from 15 ( corresponding to near perfectly oriented films ) to W ( corresponding to planar isotropic films ). Calculated magnetization configurations in the transition region for the films with small e can be characterized by a zig-zag structure [3] and the configuration for the films with a large 9 can characterized by a vortex structure [4]. The results demonstrate the gradual change of the magnetization configurations from the zig-zag structure to the vortex structure as the dispersion angle 8 increases. In a well oriented array, the intergranular exchange coupling results in smooth boundaries of the zig-zag patterns. From the simulated magnetization configurations, the track-width averaged magnetizations show that the intergranular exchange coupling yields an decrease of transition gradient. The overall shape of the track-width averaged magnetization derivative also varies with the exchange coupling constant.