Anisotropic characteristics of demagnetization curve for nanocrystalline Nd-Fe-B magnet calculated by micromagnetics

The demagnetization curves for nanocrystalline Nd-Fe-B magnets of a stoichiometric composition were calculated by making use of the finite element technique of micromagnetics. The curve, especially iHc, varies in a wide range with the direction of applied field if the grain number N is taken to be small. With the increase of N, the range becomes smaller and the average of iHc decreases and approaches a limit iHc(N = ∞). iHc for finite N is larger than, or at least equal to, iHc(N= o∞). Jr/Js is weakly affected by N and the field direction. Jr/Js(N = oo) decreases with the increase of grain size L. These are larger than the experimental values for the Nd-rich Nd2.33Fe14B1.06Si0.21 magnets by ～0.05. iHc(N = ∞) increases with the increase of L, and is close to or somewhat smaller than the experimental values of the Nd-rich magnet, as would be expected. In contrast, the curve calculated for the non-interacting grain system (Stoner-Wohlfarth model) of N 30 depends neither on the field direction nor on N.