Ultra-high coercivity of (Fe 86− x Nb x B 14 ) 0.88 Tb 0.12 bulk nanocrystalline magnets

Abstract The paper refers to hard magnetic properties of (Fe 86− x Nb x B 14 ) 0.88 Tb 0.12 bulk nanocrystalline magnets prepared using the vacuum mold suction technique. A combination of a specific chemical composition and sample preparation technology leads to a formation of dendrite grains of Tb 2 Fe 14 B hard magnetic phase. The microstructure of the obtained alloys strongly depends on both these factors. The examined alloys reveal high and ultra-high coercivity exceeding 7 T at room temperature. It was shown that the observed magnetic hardening is caused by the shape of the dendrite grains with sub-micro branches as a source of additional exchange anisotropy. Favorable hard magnetic properties occur for the alloy with 6 at.% of Nb content which corresponds to the maximum of activation enthalpy of Fe crystallization in amorphous Fe 86− x Nb x B 14 basic alloys.