Micromagnetic Simulation of Coercivity of Alnico Magnets

Abstract

A branch connecting two neighboring ferromagnetic α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -phase rods is one of the geometric factors that contributes to degradation of alnico's normally high coercivity. This letter investigates the effects of various branch geometries and dimensions on the coercivity of alnico comprehensively by using a micromagnetic simulator when the branch is assumed to be connected in either H- or U-shaped alnico structure and the magnetization reversal of the ferromagnetic α <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> -phase rod occurs by quasi-coherent rotation or curling. For the H-shaped structure, high coercivity is realized by adopting the middle-branch-connected (MBC) structure with a long branch length and width for quasi-coherent rotation, regardless of the branch thickness. For curling, the same geometric parameters are suggested except for a thick branch thickness. For the U-shaped structure with quasi-coherent rotation, a short branch thickness, width, and length, and MBC position lead a high coercivity. For curling, a short branch width but long length and edge-bridge-connected position result in a high coercivity, regardless of the branch thickness.