Optimised growth of epitaxial D019 Mn3Ge(0001) thin films via single target sputtering

Materials with chemical identity Mn3X, where X is Sn, Ga, or Ge, are Heusler alloys with intriguing properties that are fundamentally and technologically interesting. They have topological properties with a non-trivial band structure that identify them as Weyl semimetals in the bulk. Their magnetic properties, which give rise to the topological band structure through spin-orbit coupling, are determined by their Kagome lattice structure, making them chiral non-collinear antiferromagnets. Among these materials, Mn3Ge is particularly interesting because it has a larger Berry curvature, leading to a large anomalous Hall conductivity and motivating potential spintronic applications. The desirable properties are only obtained when Mn3Ge has the D019 crystal structure, so producing an easily reproducible growth recipe is the main objective of this paper. Here we show that ultra-high-quality thin films of Mn3Ge with D019 symmetry can be grown from a Mn5Ge target on an Al2O3(0001) substrate with a Ru(0001) seed layer. The expected non-collinear antiferromagnetic order was confirmed by the finding of weak zero-field magnetisation (0.0086 +/- 0.0002) mu_B/Mn that does not saturate at high magnetic fields and has a Neel temperature of (291 +/- 2) K.