Micromagnetic simulation for optimizing nanocomposite Nd2Fe14B/α-Fe permanent magnets by changing grain size and volume fraction

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 nano-composite 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 nano-composite Nd2Fe14B/alpha-Fe permanent magnet in which grain sizes and volume fractions of magnetically hard Nd2Fe14B phase and soft alpha-Fe phase vary independently, ranging in grain size from 5 nm to 40 nm and in the volume fraction of alpha-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/m(3) 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 (similar to 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.

Automated summary

This study investigates the impact of microstructure design on magnetic properties of exchange coupling nano-composite permanent magnets through micromagnetic modeling, finding that the grain size of the hard phase plays a critical role in enhancing the maximum energy product (BH)max. Additionally, simulations with a grain boundary phase show little difference compared to simulations without the grain boundary phase when the thickness of the grain boundary phase is very small, but coercivities and (BH)max decrease significantly with increasing soft phase when the thickness of the grain boundary phase is 5 nm.