(Nd,La,Ce)-Fe-B hot-deformed magnets for application of variable-magnetic-force motors

Abstract

The recent development of variable-magnetic-force (VMF) motors has raised a new demand for permanent magnets with a moderate coercivity and magnetizing field (Hmag), flat first-order reversal curves (FORCs), and high magnetization. In this study, we explored the potential of low-cost (Nd,La,Ce)-Fe-B hot-deformed magnets for the VMF motor application. We showed that the coercivity can be tuned to a desirable value (∼0.15-0.65 T) using a combined effect of intrinsic and extrinsic factors. Unlike commercial Nd-Fe-B sintered magnets, FORCs of the (Nd,La,Ce)-Fe-B hot-deformed magnets are flat. Microstructure observation and magneto-optical Kerr effect (MOKE) microscopy showed the origin of the flat FORCs is the large volume fraction of the rare-earth-rich intergranular phase in the ultra-fine grained microstructure, which acts as pinning sites against magnetic domain wall propagation. Moreover, a relatively high remanent magnetization of 1.26 T for the (Nd,La,Ce)-Fe-B hot-deformed magnet is an additional merit compared to the previously proposed sintered magnets for the VMF motor application. This work demonstrates the (Nd,La,Ce)-Fe-B hot-deformed magnets are excellent candidates for VMF motor applications and thus widens the application spectrum for low-cost (Nd,La,Ce)-Fe-B magnets with a goal of well-balanced use of critical rare earth elements.