Investigation of Magnetic Anisotropy for α-Fe/Nd₂Fe₁₄B Composition Alloy as Exchange-Spring Magnets Prepared Using Hot-Upsetting Technique

Abstract

A hot-upsetting process was applied to rapidly quenched starting ribbon powders having Nd₁₀Fe₈0Co₅B₅ alloy composition of the α-Fe/Nd₂Fe₁₄B system, with the aim of obtaining anisotropic exchange-spring magnets. Specimens fabricated at upsetting temperatures up to 950°C displayed isotropic magnetic properties, but anisotropic magnetic properties were manifested at 1000°C or higher. Specimens that exhibited anisotropy showed magnetic properties on the order of B_r = 0.3 T and H_cJ= 30 kA/m and consisted of a soft α-Fe magnetic phase and a hard Nd₂Fe₁₄B magnetic phase. Hard-phase crystals showed equiaxial morphology and reached a grain size of approximately 1μm. We observed from XRD patterns that the easy-magnetization axis of the hard-phase crystals tended to be oriented parallel to the direction of applied upsetting pressure.