Experimental approaches for micromagnetic coercivity analysis of advanced permanent magnet materials

Abstract

Although coercivity is one of the fundamental properties of permanent magnets, it has not been well understood. In this paper, micromagnetics and thermal activation magnetization reversal theories are briefly reviewed, and then our recent macroscopic and microscopic experimental approaches for thermally activated magnetization reversal in advanced Nd-Fe-B hot-deformed magnets are explained. Our experimental results are well supported by the recent atomistic spin model calculations. Moreover, the systematic micromagnetics simulation study makes much clearer the physical picture of the thermally activated magnetization reversal process in permanent magnets.

Quantitative estimation of coercive field in a ferromagnetic grain using field sweep simulation

“…where E 0 is the zero-field energy barrier and H 0 is the field for zero-energy barrier. This formula has often been employed for studies of magnetization reversal in permanent magnets [21,50,51].…”

“…Recently, n 1 for several Nd-Fe-B magnets was experimentally determined for a nucleation process [21,51] using a magnetic viscosity measurement and the Sharrock equation [56,57] (relation of coercivity vs reversal time). n 1 was also confirmed by an experiment observing the reversal probability against a field sweep [51]. n = 1 was theoretically suggested in a recent nucleation model study [58] and in a Monte Carlo study for the Nd magnet atomistic model [33].…”

“…Here, we just introduce experimental situation of coercive fields of Nd 2 Fe 14 B magnets. References [21,51] reported that H c , H 0 , and E 0 /k B were estimated for 25-200 • C in two types of hot-deformed Nd-Fe-B magnets: an as-hot-deformed…”