Kerr microscopy observation of nitrogenated Sm 2Fe 17 intermetallic compounds

Abstract

By absorbing nitrogen, the Sm 2Fe 17 compound changes its magnetic nature from planar to uniaxial anisotropy. Using magneto-optic Kerr microscopy, we have succeeded in detecting a nitride layer of Sm 2Fe 17N x formed at a surface of an Sm 2Fe 17 particle, and investigated the nitriding kinetics. With increasing nitriding time in a N 2 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 Sm 2Fe 17N 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/cm 2 for a fully nitrided compound of Sm 2Fe 17N 2.6. The calculated critical single domain size for this compound is 0.27 μm.