COERCIVITY OF SM-FE-N FERROMAGNETS PRODUCED BY THE MECHANICAL ALLOYING TECHNIQUE

Sm-Fe-N permanent magnets have been prepared by mechanical alloying of Sm and Fe powder and subsequently treating the material in a two-step process. Measurements of the minor hysteresis loops and of the initial magnetization curve were performed at room temperature. The reversible susceptibility (chi(rev)), the total susceptibility (chi(tot)) of the initial magnetization cur-ve and of the demagnetization curve, and the temperature dependence of the coercive field (H(c)) of a magnetically isotropic nanocrystalline Sm-Fe-N magnet have been measured up to a field strength of 6.4 MA/m. The anisotropy constants, K1 and K2, of Sm2Fe17Nx were deduced from the crystalline electric field calculation in the temperature range from 0 to 500 K. The critical diameter of single domain Sm-Fe-N particles was calculated to be 320 nm at room temperature. This leads to the conclusion that mechanically alloyed Sm-Fe-N is composed of single-domain particles. The temperature dependence of the coercive field of Sm-Fe-N has been analyzed within the framework of the micromagnetic models. It is concluded from these results that the nucleation process controls the coercivity mechanism of mechanically alloyed Sm-Fe-N material. The thermostability of the Sm-Fe-N magnet has also been tested.