Investigating the strain controlled epitaxial growth of Mn3Ge films through thickness modulation

Mn3Ge, a typical member of the Heusler family, has a high spin polarization and large spin Hall angle, making it a potential material for spintronic devices. Regarded as a topological Weyl semi-metal, Mn3Ge could be applied in topological spintronics owing to its special Fermi-arc-type surface states and various spin transport properties. In this study, we grew high-quality perpendicularly magnetized Mn3Gefilms through magnetron sputtering. X-ray diffraction (XRD) showed that hexagonal antiferromagnetic Mn3Ge was mixed with tetragonal ferromagnetic Mn3Ge. Thickness-dependent double-phase Mn3Ge films with large magnetic anisotropy and robust anomalous Hall effect (AHE) were obtained. The triangular spin structure of hexagonal Mn3Ge enhances the AHE; however, it shrinks the coercivity of the tetragonal ferromagnetic property. This manipulation of coexisting multi-phases comes from the strain of the substrate during growth, achieved by controlling the film thickness. Structural, magnetic, and transport measurements demonstrated stress modulation of the defect pinning, magnetic anisot-ropy, and spin transport properties. The coexistence of antiferromagnetic and ferromagnetic Mn3Ge provides the possibility of a new generation of Mn3X-based devices for applications in spin-torque memories.