Magnetization reversal process of anisotropic hot-deformed magnets observed by magneto-optical Kerr effect microscopy

Magnetization reversals of hot-deformed (HD) and eutectic alloy diffusion processed hot-deformed (DPHD) magnet with the coercivities of 0.84 T and 2.21 T, respectively, have been investigated by means of magneto-optic Kerr effect microscopy and micromagnetic simulations. In the HD magnet, magnetization reversal starts from misaligned coarse grains located at the interface of initial flakes. At a higher magnetic field, the reversed domains show cascade propagation in the vertical direction to the applied magnetic field (c-axis) through the exchange-coupled grains due to weak pinning. Although magnetization reversal also starts from misaligned grains in DPHD magnet, magnetic domains propagate along the external magnetic field because of the stray filed from reversed grains and strong pinning to the lateral direction due to the formation of non-ferromagnetic grain boundary phase hindering cascade domain wall propagation. Our micromagnetic simulation results indicate that the removal of misaligned grains in the anisotropic hot-deformed magnets combined with the formation of non-ferromagnetic grain boundary phase are the key to develop higher coercivity anisotropic hot-deformed Nd-Fe-B magnets.