Effect of strength of intergrain exchange interaction on magnetic properties of nanocomposite magnets

Micromagnetic calculation using a discrete model was applied to computer simulation of the magnetic properties of nanocomposite magnets, and the effect of the strength of the intergrain exchange interaction on magnetic properties was studied. A reduction of the strength of the intergrain exchange interaction suppressed the averaging effect of anisotropy in hard grains and increased coercivity. An excessive decrease in the strength, however, enabled magnetization in soft grains to reverse and again decreased coercivity. The maximum energy product did not increase by reducing the strength of the intergrain exchange interaction when the grain size was relatively large. On the other hand, the maximum energy product of a magnet with a relatively small grain size increased by reducing the strength of the intergrain exchange interaction. This suggests that we can obtain a large maximum energy product in a magnet with a small grain size and a suitably weak strength of the intergrain exchange interaction. Nanostructure suitable to a nanocomposite magnet was discussed based on the calculation.