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.

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

We grew Mn4−xNixN epitaxial thin films on MgO(001) by molecular beam epitaxy, as well as studied their crystalline qualities and magnetic properties. The films were decomposed into Ni8N or Mn-Ni alloys when x ≥ 2, as confirmed by X-ray diffraction and reflection high-energy electron diffraction, but this decomposition was mitigated by reducing the substrate growth temperature. The lattice constants decreased with increased Ni substitution except when the Mn ratio was high, while the crystal orientation tended to degrade. The magnetic properties were measured via vibrating sample magnetometer, and it was found that the saturation magnetization (MS) and perpendicular magnetic anisotropy (PMA) diminished with a small amount of Ni substitution. Specifically, the MS value was remarkably decreased from 86.3 ± 1.1 emu/cm 3 (Mn4N) to 19.0 ± 0.5 emu/cm 3 (Mn3.85Ni0.25N), and the magnetic anisotropy constant was decreased from approximately 0.94 to 0.027 Merg/cm 3 , respectively. The PMA vanished with further Ni substitution. Ultimately, a small MS and a PMA were simultaneously achieved with a small amount of Ni substitution. These properties support spin transfer torque, which can be applied to the emerging non-volatile memory devices using domain wall motion.