| Popis: |
The stray magnetic field distributions at the surfaces of isotropic and anisotropic NdFeB-type magnets have been imaged by magnetic force microscopy. Polished surfaces of bulk samples produced by melt-quenching, hot-rolling, and sintering were examined using two techniques which provided complementary information on the structure of the domains at the surface. For the first technique a high-coercivity magnetic tip was used, and for the second, a soft magnetic tip was used. The structures which have been observed are compared with those reported by other workers using techniques of Lorentz electron microscopy and optical Kerr microscopy and generally appear to be in good agreement. Preliminary analysis of the images collected from the hot-rolled material suggests the presence of circular ‘bubble’ domains, alongside the more regularly observed stripe domains. These appear to be reverse domains, involving only a small amount of material, which have arisen at the exposed surface to minimize the magnetostatic energy at the surface. Imaging of the die-upset material proved to be somewhat more difficult than for the other materials due to strong stray fields at the surface that affected the tip's magnetic moment during imaging. This problem was largely overcome by the use of special high-coercivity tips. The results nonetheless are in accordance with recently published Kerr micrographs for the same material. |
