Soft magnetic properties of nanocrystalline Ni3Fe and Fe75Al12.5Ge12.5

Abstract

Magnetization curves were measured on Ni₃Fe and Fe₇₅Al_12.5Ge_12.5 nanocrystals of different grain sizes. These materials were prepared by high-energy ball milling, followed by annealing at various temperatures. The alloy compositions were chosen because they have low magnetostriction in bulk form, implying that strain in the samples should have little effect on their magnetic properties. The M-H magnetization curves were used to obtain the coercivity, the maximum permeability, and the saturation magnetization. Differences in these magnetic properties were related to changes in grain size and internal RMS strain. In spite of the low bulk magnetostriction of these materials, the internal stress controlled the coercivity. The changes in permeability, however, were not as expected from the trend in grain size. We suggest that the powder morphology, plays an important role in determining the soft magnetic properties of these nanocrystalline alloys.