液体急冷法により作製したNd₁₅Fe₇₇B₈薄帯における準安定粒界相と高保磁力に対する効果

抄録

Microstructures and magnetic properties were studied of melt-spun Nd₁₅Fe₇₇B₈ ribbons with various thicknesses. High coercive force up to 1824 kA·m⁻¹ (22.8 kOe) took place for ribbons with 45∼100 μm in thickness. It was found that interspaces among Nd₂Fe₁₄B grains in these ribbons were filled by a non-magnetic phase. Electron diffraction patterns of the grain boundary phase were analyzed to reveal that this phase is of tetragonal structure with lattice constants of a=0.512 nm and c=0.801 nm. An orientation relationship was found to exist such that [001] of the boundary phase lies pallalel to the [001] direction of the host Nd₂Fe₁₄B phase.
The boundary phase is metastable, since it was decomposed into fcc-Nd and a small amount of NdFe₄B₄ phase on heating above 690 K.
Coercive force of these ribbons was discussed in terms of a nucleation controled coercivity mechanism. The smoothness of the interface between Nd₂Fe₁₄B and the boundary phase controls the nucleation behavior of reverse domains. Thus as-melt-spun ribbons exhibited smooth boundaries and high coercive force, heat-treated ones exhibiting rough boundaries and low coercive force.