Microstructure and magnetic properties of microalloyed α-Fe/Nd₂Fe₁₄B nanocomposites

The effect of minor elements (Cu, Nb, Zr and/or Ga) on the microstructure and magnetic properties of α-Fe/Nd₂Fe₁₄B nanocomposites obtained by melt-spinning Nd₈Fe₈₇B₅ based alloys has been studied by using three-dimensional atom probe and transmission electron microscopy. Cu atoms form clusters prior to the crystallization of amorphous precursors. However, Cu clusters do not act as heterogeneous nucleation sites for the α-Fe crystals; thus, Cu addition is not beneficial for reducing the grain size of α-Fe/Nd₂Fe₁₄B nanocomposites. On the other hand, Nb is effective in suppressing grain growth while annealing an partially crystallized melt-spun Nb-containing alloy. However, it was not possible to optimize the microstructures and magnetic properties by crystallizing Nb-containing amorphous precursors. The hard magnetic properties with H_c = 496 kA/m and (BH)_max = 134 kJ/m³ were obtained by adding a small amount of Zr. The coercivity was enhanced by combined addition of Zr and Ga. Zr and Ga atoms are partitioned into the Nd₂Fe₁₄B phase, and evidence for a slight enrichment of Zr atoms at the α-Fe/Nd₂Fe₁₄B interfaces has been found.