The effect of Tb doping on the magnetic properties and microstructure of a TbNdFeCoB/Fe₇Co₃ nanocomposite permanent magnet

Abstract

Melt-spun NdFeB-type nanocomposite magnetic materials are important in a number of applications, including electromagnetic sensors, magnetic resonance imaging, and voice coil motors. Herein we investigated the magnetic properties and microstructures of melt-spun Tb x Nd 10−x Fe 80 Co 4 B 6 /Fe 7 Co 3 (x=0.1, 0.2, and 0.3) ribbons by means of x-ray diffractometry, scanning electron microscopy, and magnetization experiments. Tb doping resulted in the formation of a 2:14:1 phase with a higher anisotropy field, which suppressed the separation of Fe 7 Co 3 branch crystals and improved the magnetic properties of the material. Optimum magnetic properties that include a remanence (J r ) of 0.62 T, a coercivity (H ci ) of 612.0 kA m −1 , and a maximum magnetic energy product ((BH) max ) of 94.9 kJ m −3 were obtained for the annealed Tb 0.3 Nd 9.7 Fe 80 Co 4 B 6 /Fe 7 Co 3 ribbon. Furthermore, the effective anisotropy constant, K , eff and the saturation magnetization, Ms, in the nanocomposite were determined by the LATS (law of approach to saturation) method. In this study, the values of K eff and Ms were found to lie between those of hard and soft magnetic phases, consistent with the exchangecoupling concept.