Spintronics, which is the basis of a low-power, beyond-CMOS technology for computational and memory devices, remains up to now entirely based on critical materials such as Co, heavy metals and rare-earths. Here, we show that Mn4N, a rare-earth free ferrimagnet made of abundant elements, is an exciting candidate for the development of sustainable spintronics devices. Mn4N thin films grown epitaxially on SrTiO3 substrates possess remarkable properties, such as a perpendicular magnetisation, a very high extraordinary Hall angle (2%) and smooth domain walls, at the millimeter scale. Moreover, domain walls can be moved at record speeds by spin polarised currents, in absence of spin-orbit torques. This can be explained by the large efficiency of the adiabatic spin transfer torque, due to the conjunction of a reduced magnetisation and a large spin polarisation. Finally, we show that the application of gate voltages through the SrTiO3 substrates allows modulating the Mn4N coercive field with a large efficiency.

We grow 25-nm-thick Mn4N and Co0.2Mn3.8N epitaxial films on SrTiO3(001) by molecular beam epitaxy. These films show the tetragonal structure with a tetragonal axial ratio c/a of approximately 0.99. Their magnetic properties are measured at 300 K, and perpendicular magnetic anisotropy is confirmed in both films. There is a tendency that as the Co composition increases, an anisotropy field increases, whereas saturation magnetization and uniaxial magnetic anisotropy energy decrease. First-principles calculation predicts the existence of tetragonal Mn4N phase. This explains the c/a ∼ 0.99 in the Mn4N films regardless of their film thickness and lattice mismatch with substrates used.

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.

Spin-transfer torque (STT) and spin–orbit torque (SOT) are spintronic phenomena allowing magnetization manipulation using electrical currents. Beyond their fundamental interest, they allow developing new classes of magnetic memories and logic devices, in particular based on domain wall (DW) motion. In this work, we report the study of STT-driven DW motion in ferrimagnetic manganese nickel nitride (Mn4–x Ni x N) films, in which magnetization and angular momentum compensation can be obtained by the fine adjustment of the Ni content. Large domain wall velocities, approaching 3000 m/s, are measured for Ni compositions close to the angular momentum compensation point. The reversal of the DW motion direction, observed when the compensation composition is crossed, is related to the change of direction of the angular momentum with respect to that of the spin polarization. This is confirmed by the results of ab initio band structure calculations.

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.

Ferrimagnetic Mn4N is a promising candidate for current-induced domain wall motion assisted by spin-transfer and spin–orbit torques. Mn4N can be doped to have perpendicular magnetic anisotropy (PMA) and a small spontaneous magnetization. However, the origin of the PMA of Mn4N has yet to be fully understood. Here, we investigated the relationship between the ratios of the perpendicular lattice constant c to the in-plane lattice constant a of Mn4N epitaxial thin films (c/a) and the uniaxial magnetic anisotropic constant (Ku) in Mn4N thin films grown on MgO(001), SrTiO3(001), and LaAlO3(001) substrates. The lattice mismatches between Mn4N and these substrates are approximately −6%, −0.1%, and +2%, respectively. All the Mn4N thin films had PMA and in-plane tensile distortion (c/a < 1) regardless of the Mn4N thickness and substrate. Although the magnitude of c/a depended on several factors, such as the Mn4N layer thickness and substrate, we found a strong correlation between c/a and Ku; Ku increased markedly when c/a deviated from 1. This result indicates that the origin of PMA is tensile distortion in Mn4N films; hence, it might be possible to control the magnitude of Ku by tuning c/a through the Mn4N layer thickness and the substrate.

Off-stoichiometry, structural-polar disorder and piezoelectricity enhancement in pre-MPB lead-free Na 0.5 Bi 0.5 TiO 3 -BaTiO 3 piezoceramic