Anisotropic exchange in Nd–Fe–B permanent magnets

The exchange is critical for designing high-performance Nd–Fe–B permanent magnets. Here we demonstrate through multiscale simulations that the exchange in Nd–Fe–B magnets, including bulk exchange stiffness (Ae) in Nd2Fe14B phase and interface exchange coupling strength (Jint) between Nd2Fe14B and grain boundary (GB), is strongly anisotropic. Ae is larger along crystallographic a/b axis than along c axis. Even when the GB FexNd1–x has the same composition, Jint for (100) interface is much higher than that for (001) interface. The discovered anisotropic exchange is shown to have profound influence on the coercivity. These findings enable more freedom in designing Nd–Fe–B magnets by tuning exchange.