Tuning the magnetic anisotropy in artificially layered Mn 3 GaN / Mn 3 Ga superlattices

Artificially layered superlattices with two distinct spin structures offer new opportunities for manipulation of magnetic properties and interfacial spin configurations. We have grown epitaxial, coherent superlattices of ferrimagnetic ${\mathrm{Mn}}₃\mathrm{Ga}$ and noncollinear antiferromagnetic ${\mathrm{Mn}}₃\mathrm{GaN}$. The out-of-plane ferrimagnetism of the ${\mathrm{Mn}}₃\mathrm{Ga}$ layer, and the Berry-phase charge to spin current generation by the noncollinear antiferromagnetic ${\mathrm{Mn}}₃\mathrm{GaN}$ layer, provide a unique combination for spintronic applications. Reactive magnetron sputtering growth resulted in abrupt transitions between the two layers through controlling the ${\mathrm{N}}₂$ flow. X-ray diffraction and cross-sectional scanning transmission electron microscopy images demonstrate clean layering and consistent modulation wavelengths, with interfacial roughness less than one unit cell. This allows investigation of the interfacial magnetic interactions. Through a combination of superconducting quantum interference device magnetometry and polarized neutron reflectometry we show that ${\mathrm{Mn}}₃\mathrm{Ga}/{\mathrm{Mn}}₃\mathrm{GaN}$ superlattice structures have the out-of-plane magnetic anisotropy decreased compared to ${\mathrm{Mn}}₃\mathrm{Ga}$ single-layer films. This softening is primarily a result of reduced anisotropy energy at the interface and is linked to the ${\mathrm{Mn}}₃\mathrm{GaN}$ layer. This superlattice structure provides a platform for devices that use out-of-plane spin torques generated from an antiferromagnetic material to switch the net magnetic moment of a ferrimagnetic material. Our results demonstrate the tunability of magnetic anisotropy to allow for optimal balancing of the switching power and thermal stability in spintronic heterostructures.