KERR MICROSCOPY OBSERVATION OF NITROGENATED SM2FE17 INTERMETALLIC COMPOUNDS

By absorbing nitrogen, the Sm2Fe17 compound changes its magnetic nature from planar to uniaxial anisotropy. Using magneto-optic Kerr microscopy, we have succeeded in detecting a nitride layer of Sm2Fe17N(x) formed at a surface of an Sm2Fe17 particle, and investigated the nitriding kinetics. With increasing nitriding time in a N2 atmosphere, the surface nitride increased its thickness keeping a constant nitrogen concentration. An additional annealing in an Ar atmosphere was found to be effective in homogenizing the charged nitrogen. Magnetic domain pattern of the SM2Fe17N(x) compound became finer as the nitrogen content decreased. Domain models for different x are given by using magnetic properties measured on magnetically-aligned particles. The domain wall energy was estimated to be 28 erg/cm2 for a fully nitrided compound of Sm2Fe17N2.6. The calculated critical single domain size for this compound is 0.27-mu-m.