Development of Zn-bonded Sm-Fe-N permanent magnet and magnetic powders with high magnetic coercivity

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We have tried to establish permanent powders with high magnetic coercivity at high temperatures by using the Sm-Fe-N compound, which has high magnetic anisotropy and high Curie tepmperature. In particular, the present work is directed toward the development of the magnetic coercivity by coating the powders of Sm-Fe-N compound with zinc films, by using vapor deposition and electro-chemical deposition. We have obtained as follows.1.We have determined optical conditions of temperature, pressure and time to prepare the high-coercivity material by the plasma sintering method, by using starting materials of the Sm-Fe-N and zinc powders. As a result we obtained the maximum coercivity of 20kOe at 420ﾟC,5,000kg/cm^2, and for 5 min. The result shows that the plasma sintering is a powerful tool to establish high coercivity in a short time and at a low pressure, compared with ordinary sintering methods.2.We have carried out zinc-coating the Sm-Fe-N powders with an average sizes of 20mum (rough powders) and 3mum (fine powders), by using vapor deposition and electro-chemical deposition, and then sintered by the plasma sintering method. As a result we have obtained the improvement of the magnetic coercivity by zinc coating for the rough powders, but no improvement for the fine powders. It is concluded that the development of new methods of zinc coating is necessary.3.We have succeeded in high-resolution transmission electron microscopy observations of Sm-Fe-N powders including Mn, which are expected to be high coercivity of pinning-type, and found that the pinning of magnetic domain walls is produced by fine-grained crystals with about 10 nm in diameter.