Micromagnetic simulation for optimizing nanocomposite Nd2Fe14B/[formula omitted]-Fe permanent magnets by changing grain size and volume fraction

Abstract

Nanocomposite permanent magnets can achieve excellent magnetic properties due to the hardening of a soft phase by hard phase within the length of exchange coupling. The performance of exchange coupling nanocomposite magnets can be optimized through the design of appropriate microstructure by micromagnetic modeling. In this study, we performed a micromagnetic simulation for isotropic exchange coupling nanocomposite Nd2Fe14B/α-Fe permanent magnet in which grain sizes and volume fractions of magnetically hard Nd2Fe14B phase and soft α-Fe phase vary independently, ranging in grain size from 5 nm to 40 nm and in the volume fraction of α-Fe from 10% to 60%. When the grain size of the hard phase is 5 nm, and that of the soft phase is 10 nm, respectively, with the volume fraction of the soft phase of 30%, the highest (BH)max of 197 kJ/m3 can be reached. Furthermore, considering the effects of the grain sizes of the hard and soft phases, we suggest that the grain size of the hard phase plays a more critical role in enhancing maximum energy product (BH)max. The micromagnetic modeling with the variation of grain size and volume faction has been performed with a grain boundary (GB) phase. It was found that when the thickness of the GB phase is very small (~1nm), there is little difference between the simulated results with the GB phase and without GB phase. On the other hand, the coercivities and (BH)max decrease significantly due to the increase of soft phase when the thickness of GB phase is 5 nm.