Experimental and computational analysis of the two-step demagnetization behavior of the surface grains of sintered Nd-Fe-B magnets

The two-step demagnetization behavior was observed before the coercive field of a sintered Nd-Fe-B magnet with a large specific surface (S/V). The squareness factor of the demagnetization curve and the energy product decreased with the increase in the S/V, while the remanence and the coercivity were relatively independent of the S/V. The magneto-optical Kerr effect was used to study the magnetic properties of the magnet surface. The surface magnetization switched freely, while the bulk magnetization remained unchanged under a low cyclic magnetic field. Micromagnetic simulations revealed that the anti-demagnetization abilities of grains at the polar surface perpendicular to the c-axis were larger than those at the lateral surface parallel to the c-axis. The different anti-demagnetization abilities of the surface grains induced the initial two-step demagnetization behavior. Published by AIP Publishing.