Influence of defect thickness on the angular dependence of coercivity in   rare-earth permanent magnets
  The coercive field and angular dependence of the coercive field of single-grain Nd$_{2}$Fe$_{14}$B 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. 
Simon Bance, Harald Oezelt, Thomas Schrefl, Georgeta Ciuta, Nora M.   Dempsey, Dominique Givord, Michael Winklhofer, Gino Hr...
cond-mat.mtrl-sci