Residual Amorphous Phase in a Fe/NdFeB Nanoconipositie Hard Magnets

Abstract

ABSTRACTA residual amorphous phase can be observed when Nd content is less than 8 at% in a a Fe/NdFeB nanocomposite with various additional elements which was prepared by melt-spinning and heat treatment. The surface velocity of the single-roller melt-spinner for optimal coercive force (Hcj) was 10-15 m/s. By adding Nb, Hcj increases monotonically. Nearly homogeneous crystal size of around 5 nm is observed in a sample composition of NdxFex Cox Nb2,B2 With Nd=8 at%, the maximum Hcj is as large as 575kA/m (7.22kOe) at Nb=2.5 at%, and the best (BH)max is 154kJ/m3 (19.4MGOe) at Nb=0.5 at% in optimally heat-treated and pulse-current magnetized samples. By high-resolution transmission electron microscopy, a residual amorphous phase is observed in all alloy ribbons with Nd=8 at%, which shows soft magnetic properties and is thought to act as a crystal growth inhibitor. To estimate the existing ratio of the amorphous phase and crystallized phases, the Mössbauer effect has been studied. It was found that the ratio of the crystallized Nd2Fe14B1 phase increases with increasing Nb content and that several wt% of the residual amorphous phase is certified. Epoxy-resin bonded magnets were prepared by compression molding, and revealed that, comparing to the MQP bonded magnet using conventional MQP-B powder, their (BH)max are in the same order of 72kJ/m3 (9MGOe), and magnetization at lower magnetic field than 800kA/m (10kOe) is superior. Initial flux loss at 100°C for 1.8ks, however, is in the range of 3-8% depending on Nb contents.