Effect of Magnetic Inhomogeneity on Magnetization Reversal in Sintered Nd-Fe-B Magnet –Numerical Approach–

Abstract

We present extensive studies on feedback-induced instabilities in semiconductor lasers (SLs) subject to delayed optical feedback. We demonstrate that a sufficient reduction of the linewidth enhancement factor α changes the dynamical structure of the system such that permanent emission in a stable emission state is achieved. This behaviour can be well understood on the basis of the Lang-Kobayashi rate equation model. We give first experimental evidence for its major theoretical predictions concerning the stable emission state and investigate the robustness of this stable state against external perturbations. We demonstrate that noise-induced escape from the basin of attraction of the stable state shows similarities to the classical problem of thermally induced escape from a potential well. Thus, we have developed and realized experimentally an efficient concept to avoid and stabilize feedback-induced instabilities in SLs.

Computer simulation of coercivity improvement due to microstructural refinement

“…2,3,17 A collective effect of large non-magnetic phases located at the corners of Nd 2 Fe 14 B grains has also been reported for a sintered magnet by computer simulations based on micromagnetic theory. 18 However, these micromagnetic simulations have not clearly determined the effects of the size of the non-magnetic phases.…”

“…1 Therefore, clarification of the origins of low coercivity is an important issue for the further improvement of coercivity. For example, a reduced [2][3][4] or negative 5 magnetic anisotropy constant at grain surfaces, the existence of ferromagnetic grain boundaries, 6 and a strong local demagnetizing field 7 have been discussed as candidate origins. It has also been reported that coercivity increases with decreasing grain size.…”

Numerical Study of Enhanced Coercivity of a Magnetically Hard Grain With Thin Surface Layers Due to Antiferromagnetic Coupling

“…We used Nd 2 Fe 14 B as the hard grain. We set K u of the IP layer to zero as a first-order approximation [13], although various distributions of K u have been employed in previous investigations [13,14,16,17]. Employing another distribution may change the optimal SF layer thickness but it will not affect the general tendency of H c .…”