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 initia l magnetization curve were performed at room temperature. The reversib le susceptibility (chi(rev)), the total susceptibility (chi(tot)) of t he initial magnetization cur-ve and of the demagnetization curve, and the temperature dependence of the coercive field (H(c)) of a magnetica lly 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 si ngle domain Sm-Fe-N particles was calculated to be 320 nm at room temp erature. This leads to the conclusion that mechanically alloyed Sm-Fe- N is composed of single-domain particles. The temperature dependence o f 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 mechanical ly alloyed Sm-Fe-N material. The thermostability of the Sm-Fe-N magnet has also been tested.