δM plots of nanocrystalline hard magnetic alloys

Magnetic properties of nanocrystalline hard magnetic alloys such as coercivity and maximum energy product are strongly depended on microstructure and interactions between grains. There are a lot of advanced experimental techniques for microstructure characterization but the analysis of intergrain interactions is still challenging. One of the wide-spread methods for doing that is plotting delta M(H). This work is aimed to elucidate how different factors effect delta M(H) plots for high-anisotropy nanocrystalline alloys. Specifically, changes of delta M(H) plots caused by both intergrain exchange and magnetostatic interactions, grain size dispersion, and demagnetization factor are analyzed systematically using macrospin-based simulations. It is demonstrated that all these factors should be considered for a reliable evaluation of exchange coupling in alloys. A concept of such analysis is presented and applied to rapidly quenched Nd-FeCo-B alloy.