Micromagnetic study for optimum performance of isotropic Nd2Fe14B/α-Fe nanocomposite bulk magnets

Abstract

Abstract The nanocomposite magnets attract great interest in the study of high-performance magnets. Here, the micromagnetic simulations have been performed to investigate the effects of various microstructural factors such as grain geometry, grain size, and volume fraction on the performance of a soft-in-hard-matrix nanostructured Nd2Fe14B/α-Fe isotropic magnet. It is found that there is very little dependence of remanence on the geometry of the soft phase. The coercivity decreases with increasing the soft grain size, whereas it has a variation tendency depending on the size of hard grain size. In contrast to a significant role of soft-sphere geometry in anisotropic nanocomposites (Skomski et al 2013 IEEE Trans. Magn. 49 3215), the energy product of the soft-sphere system simulated here is slightly increased ( ⩽ 8 kJ m−3), compared with that of the soft-cylinder system. In the meantime, a significant enhancement in energy product with increasing the soft grain size is observed only when the hard grain size is less than 15 nm. Our simulation predicts the highest energy product of 347 kJ m−3 with a hard grain size of 5 nm and a soft-sphere size of 12.4 nm (30 vol% of the soft phase). It is shown that the effective magnetocrystalline anisotropy is responsible for the variation in coercivity, based on its quantitative evaluation for the soft-sphere system.