The use of epitaxial layers for domain wall-based spintronic applications is often hampered by the presence of pinning sites. Here, we show that when depositing Mn4N(10 nm) epitaxial films, the replacement of MgO(001) by SrTiO3(001) substrates allows minimizing the misfit, and to obtain an improved crystalline quality, a sharper switching, a full remanence, a high anisotropy and remarkable millimeter-sized magnetic domains, with straight and smooth domain walls. In a context of rising interest for current-induced domain wall motion in rare-2 earth ferrimagnets, we show that Mn4N/SrTiO3, which is rare-earth free, constitutes a very promising ferrimagnetic system for current-induced domain wall motion.

Epitaxial Fe4-xMnxN (x = 0, 1, 2, 3, and 4) thin films were successfully grown on MgO(001) single-crystal substrates by molecular beam epitaxy, and their crystalline qualities and magnetic properties were investigated. It was found that the lattice constants of Fe4-xMnxN obtained from X-ray diffraction measurement increased with the Mn content. The ratio of the perpendicular lattice constant c to the in-plane lattice constant a of Fe4-xMnxN was found to be about 0.99 at x ≥ 2. The magnetic properties evaluated using a vibrating sample magnetometer at room temperature revealed that all of the Fe4-xMnxN films exhibited ferromagnetic behavior regardless of the value of x. In addition, the saturation magnetization decreased non-linearly as the Mn content increased. Finally, FeMn3N and Mn4N exhibited perpendicular anisotropy and their uniaxial magnetic anisotropy energies were 2.2 × 10 5 and 7.5 × 10 5 erg/cm 3 , respectively.

The 20-60 nm-thick epitaxial Ni x Fe 4-x N (x ¼ 0, 1, 3, and 4) films were successfully fabricated on SrTiO 3 (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 ¼ 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 Ni 3 FeN film was estimated to be 266 K from the temperature dependence of magnetization. The Ni 4 N film was not ferromagnetic but paramagnetic due to its low degree of order of N site. Published by AIP Publishing.

We grew 50 nm-thick NixFe4−xN (x = 1 and 3) epitaxial films on a SrTiO3(001) single-crystal substrate by molecular beam epitaxy and measured their anisotropic magnetoresistance (AMR) ratios rAMR in the temperature range of 5–300 K with current directions set along either NixFe4−xN [100] or [110]. A negative rAMR was obtained up to 200 K or higher. Their magnitude |rAMR| increased with decreasing temperature. From the negative AMR effect and the negative spin-polarization of density of states for NixFe4−xN at the Fermi level, it can be stated that the minority spin transport is dominant in NixFe4−xN, similar to Fe4N and Co3FeN. The rAMR depends on the current direction that arises from the current direction dependence of s-d scattering. In the case of Ni3FeN, the rAMR decreased to nearly zero at 260 K. This temperature agreed well with the Curie temperature determined from the temperature dependence of magnetization. The AMR curves were reproduced well by using both cos2ϕ and cos4ϕ components below 100 K, whereas a cos2ϕ component was enough to fit those obtained above 100 K. It is assumed that the tetragonal crystal field was enhanced at low temperatures (<100 K) similar to Fe4N (<50 K).

We successfully grew a single-phase tetragonal FeNiN film with an equiatomic ratio of Fe, Ni, and N on a MgO(001) substrate by molecular beam epitaxy. We then demonstrated the formation of Fe 2 Ni 2 N films by extracting N atoms from the FeNiN film. These results suggested that Fe and Ni atoms in the Fe 2 Ni 2 N film were L1 0 -ordered along the film plane direction because of the a-axis orientation growth of the FeNiN film on the MgO(001) substrate.