Epitaxial growth and magnetic properties of Ni_xFe_{4- x}N (x = 0, 1, 3, and 4) films on SrTiO₃(001) substrates

The 20-60 nm-thick epitaxial Ni_xFe_{4- x}N (x = 0, 1, 3, and 4) films were successfully fabricated on SrTiO₃(001) single-crystal substrates by alternating the substrate temperature (T_sub), and their crystalline qualities and magnetic properties were investigated. It was found that the crystal orientation and the degree of order of N site were improved with the increase of T_sub for x = 1 and 3. The lattice constant and saturation magnetization decreased as the Ni content increased. This tendency was in good agreement with first-principle calculation. Curie temperature of the Ni₃FeN film was estimated to be 266 K from the temperature dependence of magnetization. The Ni₄N film was not ferromagnetic but paramagnetic due to its low degree of order of N site.