Magnetic force microscope study on anisotropic NdFeB permanent magnets

NdFeB permanent magnets prepared by powder metallurgy were investigated using magnetic force microscopy (MFM). The excellent MFM images of sample along the surfaces parallel and perpendicular to the alignment axis were collected respectively. The results show the necessity of annealing procedure in the preparation of the samples to remove the polishing surface stress and to illustrate the real magnetic domain structure, so that the much information about both the magnetic structure and the topographic microstructure is obtained. The hard MFM tip is verified to be effective for this material especially for the sample with the examined surface parallel to alignment axis. By analyzing these well-captured magnetic force images, magnetic domains and alignment degree as well as the topographic information such as grain size and the nonmagnetic phases at the grain boundaries were demonstrated.