Reducing the Eddy Current Losses in Nd–Fe–B Magnets Through Si Addition

Electric motors that use neodymium–iron–boron (Nd–Fe–B) magnets are at the forefront of global efforts to reduce greenhouse gas emissions. However, a major problem associated with these motors is thermal demagnetization driven by eddy current (EC) losses in the magnets; the relatively low electrical resistivity of Nd–Fe–B magnets means that the magnetic fields in the motor generate considerable EC losses. In this study, Nd–Fe–B magnets with 0–20 wt% Si additives were produced through hot pressing to investigate the effects of Si addition on magnetic properties and electrical resistivity. Small amounts of Si significantly increased electrical resistivity without negatively affecting the magnetic properties. The high coercivity of the Nd–Fe–B magnets, 12.5 kOe, did not decrease even in the presence of up to 15 wt% Si content. The electrical resistivity of Nd–Fe–B magnets increased monotonically as the Si content increased, from 1.43 μΩm for pure Nd–Fe–B magnets to 8.17 μΩm with 20% Si. As the electrical resistivity increased, the associated EC losses decreased; the estimated EC losses were halved with the addition of ~8 wt% Si, and further decreased to one-third through the addition of ~12 wt% Si, while simultaneously maintaining high coercivity.