Computer simulation of spin reorientations in polycrystalline materials—application to R2Fe14B (abstract)

Abstract

The easy direction of magnetization (DOM) is an extremely important property of a magnetic material, in regards to both permanent magnet and recording applications. In many magnetic materials, most notably Nd2Fe14B, the DOM is temperature dependent. When utilizing methods which permit the orientation of either a single crystal or pseudo-single crystal to be rigidly constrained (e.g., VSM and extraction), it is possible to determine the temperature dependence of the DOM directly. However, the determination of spin reorientation temperatures with powder samples is not always straightforward. In some cases, a peak is observed in the magnetization versus temperature curve, while in others either a drop or an increase is observed. Using a two-dimensional, two-crystallite grain as a model and assumed temperature dependencies of the anisotropy constants, K1 and K2, it is shown that these peaks and other features can be explained by polycrystalline particles (or, equivalently, imperfect alignment of the powder). It is further shown that spin reorientation temperatures are invariably characterized by the inflection points in the low-field magnetization versus temperature curve. Examples of such curves obtained from a Faraday balance for Nd2Fe12Si2B and Pr2Co14B are given.