Tuning the magnetic anisotropy in artificially layered Mn3GaN/Mn3Ga 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 Mn3Ga and noncollinear antiferromagnetic Mn3GaN. The out-of-plane ferrimagnetism of the Mn3Ga layer, and the Berry-phase charge to spin current generation by the noncollinear antiferromagnetic Mn3GaN layer, provide a unique combination for spintronic applications. Reactive magnetron sputtering growth resulted in abrupt transitions between the two layers through controlling the N2 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 Mn3Ga/Mn3GaN superlattice structures have the out-of-plane magnetic anisotropy decreased compared to Mn3Ga single-layer films. This softening is primarily a result of reduced anisotropy energy at the interface and is linked to the Mn3GaN 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.