Domain structure of sintered SmCo₅ magnets studied by magnetic force microscopy

The domain structure of sintered SmCo₅ permanent magnets at the surface perpendicular to the alignment axis was investigated by magnetic force microscopy (MFM). The main domains forming a maze pattern of typically 3–5 μm in width and surface reverse spikes of typically 1–2 μm in size are observed. This coarse domain structure is similar to those present in sufficiently thick uniaxial crystals with strong magnetocrystalline anisotropy, reported in earlier investigations performed by Bitter pattern method or magneto-optic Kerr microscopy. In addition to the coarse domain structure, a complicated system of the fine surface domains of 10–200 nm in width is observed. The thickness of the zone below the surface filled with these fine scale domains is estimated to be 100 nm and their presence is related to the reduction of the magnetostatic energy close to the specimen surface. Practically no correlation between the magnetic domain structure and the surface topography, the latter revealed by atomic force microscopy, was observed. The high spatial resolution and high surface sensitivity of the MFM technique are demonstrated.