Magnetic properties of anisotropic bonded NdFeB/SmCo permanent magnets

Abstract

Anisotropic bonded NdFeB permanent magnets have wide potential applications in the areas such as brushless DC motors, spindle motors, and stepping motors due to their excellent processing property and high magnetic properties. Anisotropic NdFeB bonded magnets prepared by hydrogen-disproportionation–desorption-recombination (HDDR) process have large energy product at room temperature. However, they are not stable at ∼100°C, which is the working temperature of many electric motors. In order to improve their thermal stability, we developed bonded NdFeB/SmCo magnets and investigated the effects of powder particle size and SmCo content on their magnetic properties. We proposed a model to clarify the filling effect of the powder, which played a key role in the enhanced (BH)_max when reducing the SmCo particle size. As for the SmCo content, the bonded magnets showed improved (BH)_max at 100°C-150°C and thermal stability with the increase of SmCo content. And through adjusting the SmCo content, the remanence temperature coefficient and coercivity temperature coefficient from 25-150°C were able to be regulated in the range of -0.14%/°C to -0.04%/°C and -0.51%/°C to -0.14%/°C, respectively. This work provides a design strategy and a facile route to improve the magnetic properties and thermal stability of the bonded magnets.