Indirect Observation of Inner Domain Structure in Nd2Fe14B Sintered Magnets

Abstract

Domain structures in sintered Nd2Fe14B magnets were studied using Kerr effect microscopy (KEM) and magneto-force microscopy (MFM). In the direction perpendicular to the crystal c-axis (c-plane), a fine maze domain structure was observed using KEM, but an only unclear complex structure can be obtained using MFM. After 5T pulse magnetization, both observation methods gave clear monotonous images of many magnetized grains and local fine domain structures with strong contrast in limited numbers of grains. On the other hand, in the direction of parallel to the c-axis (in a sense, a-plane), only bright or dark grains as a whole grain, were observed using both methods. These observations can be explained as that the surface demagnetized grains have a role of permeable medium of the magnetic fluxes from the inner domains. As a conclusion, when the inner grains generate sufficient magnetic fluxes to magnetize the surface no-coercive grains, the inner domain structures of the sintered Nd2Fe14B magnets can be observed using KEM and MFM.