Abstract
Exchange spring magnets are a new class of permanent magnets consisting of exchange coupled hard and soft magnetic phases at nano meter scale. Such an exchange coupling helps these magnets to exhibit high coercive force as well as high saturation magnetization, resulting in a higher energy product. Recent surge in the research interest in this field has shown that the nitrides of rare earth-iron compound to exhibit good magnetic properties. Also, the application of mechanical alloying technique for the synthesis of the rare earth-iron compound is found to be more versatile. In the present study we have mechanically alloyed SmxFe100-X (X=7, 9, 11, 13). In the as milled condition α-Fe was found to co-exist with an amorphous phase. Heat treating the mechanically alloyed powder resulted in the formation of Sm2Fe17 compound (hard phase) and α-Fe (soft phase). The formation of the hard phase as a function of Sm content and heat treatment temperature is studied. The heat treated samples were nitrided for different duration and at various temperatures. The major and the minor hysterysis loops of these nitrided samples were measured and their magnetic properties were studied. Good magnetic properties were observed for alloys with 9at.% Sm. Improvements in the magnetic properties and thermal stabilities of the hard phase is studied by the substitution of Co, Cr and Si for Fe. It was found that Co substitution for Fe increases both the remanence and the coercivity, resulting in a higher energy product.
