Computer Simulation of Magnetic Properties of Nanocomposite Magnets

Magnetic properties of a model nanocomposite magnet, which is composed of magnetically soft and hard grains, were calculated by means of computer simulation, and the effects of the strength of intergrain exchange interaction and the amount of soft grains on them were studied. The presence of soft grains and the intergrain exchange coupling enhanced the remanence remarkably, and the remanence over 0.8Ms was obtained in the model magnets containing more than 25% soft grains in volume. The calculated coercivity vs. the strength of the exchange interaction curves showed a peak at a critical strength of the exchange interaction, although the remanence increased monotonically with increase in the strength of the exchange interaction. Thus the maximum energy product also reached a peak around the same critical strength. The calculated maximum energy product exceeded 300 kJ/m3 for the magnet composed of Fe3B and Nd2Fe14B and 400 kJ/m3 for one composed of α-Fe and Nd2Fe14B. Dispersion of the strength of the exchange coupling reduced the energy product significantly, which suggests that homogeneous microstructure is needed to obtain nanocomposite magnets with superior magnetic properties.