MAGNETIC-ANISOTROPY AND SOFT MAGNETISM OF IRON NITRIDE THIN-FILMS PREPARED BY FACING-TARGET SPUTTERING

Iron nitride thin films have been prepared at various nitrogen-gas pressures (P(N2)) on a heated substrate by using a facing-target sputtering (FTS) system, and their crystallographic characteristics and magnetic properties have been investigated. Total gas pressure (P(N2) + P(Ar)) was set at 2 mTorr. M(S) for the films prepared at P(N2) below 0.05 mTorr was slightly higher than 1700 emu/cc with scattering and did not show apparent dependence on P(N2). These films exhibited a bcc structure, and the lattice constant was about 2.875 angstrom, which was larger than that of bulk iron. Large values of compressive stress were observed in these films. The films prepared with pure argon gas exhibited isotropic magnetic properties in the film plane, while the films with P(N2) above 0.07 mTorr exhibited magnetic anisotropy in the film plane. The direction of the easy axis was parallel to the magnetic stray field in the FTS system. The films with soft magnetism were prepared at P(N2) around 0.1 mTorr, which corresponded to the onset of the growth of gamma'-Fe4N. A minimum H(c) of 0.5 Oe in the hard axis and M(s) of 1700 emu/cc were obtained in these films.