Current status of room temperature magnetic compensation in impurity-doped Mn₄N epitaxial thin films

Mn₄N, a ferrimagnet that does not contain rare-earth elements, possesses attractive properties for spintronics applications. In particular, Mn₄N epitaxial films exhibit a small spontaneous magnetization of about 100 kA m^-1, a large spin polarization (p = 0.8), and large perpendicular magnetic anisotropy with a magnetic anisotropy constant of approximately 10⁵ J m^-3. More importantly, achieving magnetic compensation at room temperature is possible through impurity doping. This property is particularly significant for spin-torque-based spintronics applications. In the vicinity of the magnetization and/or angular momentum compensation points, magnetization dynamics can be substantially accelerated, enabling high-speed switching and domain wall motion. This article surveys the magnetic properties of impurity-doped Mn₄N epitaxial films grown on SrTiO₃(001) substrates, highlighting recent results obtained with Cu-, Ag-, Au-, and Pd-doped Mn₄N films in comparison with Ni- and Cr-doped Mn₄N films. Furthermore, with a view to device applications of Mn₄N, we present the formation of ultrathin (~4 nm) Pt epitaxial films with a <100> orientation on MgO (001), which is essential for injecting spins into Mn₄N-based overlayers by utilizing the spin Hall effect of heavy metals.