The coercive field and angular dependence of the coercive field of single-grain Nd2Fe14B permanent magnets are computed using finite element micromagnetics. It is shown that the thickness of surface defects plays a critical role in determining the reversal process. For small defect thicknesses reversal is heavily driven by nucleation, whereas with increasing defect thickness domain wall de-pinning becomes more important. This change results in an observable shift between two well-known behavioral models. A similar trend is observed in experimental measurements of bulk samples, where a Nd-Cu infiltration process has been used to enhance coercivity by modifying the grain boundaries. When account is taken of the imperfect grain alignment of real magnets, the single-grain computed results appears to closely match experimental behaviour.
@article{arxiv.1603.08248,
title = {Influence of defect thickness on the angular dependence of coercivity in rare-earth permanent magnets},
author = {Simon Bance and Harald Oezelt and Thomas Schrefl and Georgeta Ciuta and Nora M. Dempsey and Dominique Givord and Michael Winklhofer and Gino Hrkac and Gergely Zimanyi and Oliver Gutfleisch and Thomas G. Woodcock and Tetsuya Shoji and Masao Yano and Akira Kato and Akira Manabe},
journal= {arXiv preprint arXiv:1603.08248},
year = {2016}
}