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

High coercivity is an important property of permanent magnets for application in energy conversion devices. The Nd magnet, Nd2Fe14B, is a typical material. Because coercivity is a long-time relaxation phenomenon, which originates from a strong metastable magnetic state, it is difficult to estimate coercive field (coercive force) studying the time evolution dynamics simulation of a model with atomistic parameters under the limitation of the simulation time. In our recent study [M. Nishino et al., Phys. Rev. B 102, 020413(R) (2020)], we presented a method to estimate coercivity using a statistical method to extend the limitation of simulation time and evaluated appropriately the coercive field of a single grain of the Nd magnet. In the present study, we propose an alternative method to estimate coercivity more conveniently using the field-dependent survival (nonreversal) probability generated by a time evolution simulation under a field sweep. We demonstrate that the coercive field of the single grain can be estimated. In this method, not only coercive field but also the zero-field energy barrier and field for the zero-energy barrier can be estimated. We discuss detailed features of the estimation of these quantities.