Micromagnetic Simulation of Influence of Microstructure Parameters on Realization of High Coercivity State in Hard-Magnetic MnAl Alloys

Micromagnetic simulation was employed to investigate the influence of microstructure parameters on the realization of high coercivity in nanocrystalline MnAl alloys, a promising alternative to rare-earth-based permanent magnets. The study focused on the effects of crystallite size (10–200 nm) and intergrain layer properties (non-ferromagnetic and soft-magnetic) on coercive force (Hc) and remanent magnetization (Mr/Ms). Simulations were performed using GPU-accelerated mumax3 software, with material parameters set to match MnAl (Ku1 = 1.5 MJ/m3, Aex = 19.9 pJ/m, Msat = 0.66 MA/m). Results revealed that the highest coercivity (μ0Hc = 0.5 T) was achieved for crystallite sizes between 30–90 nm, consistent with experimental literature. The shape of the crystallites (cubic vs. cylindrical) showed negligible influence except for larger sizes (200 nm). For non-ferromagnetic interlayers, coercivity peaked at 0.52 T with a 7-nm thickness, attributed to the magnetic isolation of crystallites, while thicker layers with reduced Hc could be associated with changes in magnetic interaction between crystallites. In contrast, soft-magnetic interlayers (α-Fe) caused a monotonic decline in both Hc and Mr/Ms with increasing thickness. These findings provide critical insights for optimizing MnAl-based magnets, highlighting the importance of crystallite size control and interlayer engineering in achieving high coercivity.