MAGNETIC-PROPERTIES OF SM2FE17NX POWDERS PREPARED BY MECHANICAL GRINDING

Using Sm2.5Fe17 alloy powder of -100 mesh, the preparation of Sm2Fe17N x magnetic powder whose grain size is finer than the single magnetic d omain size was carried out by mechanical grinding (MG) and subsequent heat treatments for crystallization, nitriding and annealing. The effe cts of MG time and heat treatment on the factors such as the grain siz e, nitrogen and oxygen content, the precipitation of alpha-Fe and magn etic properties have been investigated. The results obtained are summa rized as follows: (1) The grain size of powders after MG was about 10- 30 nm and it was extremely finer in comparison with the single magneti c domain size of about 300 nm. Although the grain size was coarsened b y the subsequent heat treatments, it was about 50 nm even after anneal ing. (2) The precipitation of alpha-Fe was caused by the oxidation of powder, and it was confirmed that the oxygen content of the powder sho uld be lower than 9000 ppm in order to prevent the alpha-Fe precipitat ion. (3) The maximum coercivity of 2.24 MA . m(-1) was obtained under the following condition; i.e., MG time: 108 ks, crystallization: at 10 23 K for 1.8 ks, nitriding: at 723 K for 129.6 ks and annealing: at 62 3 K for 7.2 ks in N-2.