Effect of Bi-Axial Strain on Cation Octahedral Rotations and Electronic Band Structure of the Antiperovskite Mn3GaN

Strain-engineering is a powerful technique to control properties of perovskite oxides. The effect of bi-axial strain is effectively a rotation/tilt of the oxygen octahedra, altering bond angles and lengths. Antiperovskite materials, functional materials that can possess properties such as antiferromagnetism, superconductivity and topological effects, have a perovskite crystal structure. However, a cation is occupying the oxide anion position while the perovskite B-site is occupied by an anion. Recent progress in thin film deposition has advanced heterostructures of antiperovskites with oxide perovskites and other quantum materials. Here, a density functional theory (DFT) study of the effect of bi-axial strain on the cubic antiperovskite Mn3GaN is presented. Mn3GaN is antiferromagnetic with the Mn spins ordered in a Kagome Γ^5g structure. Contrary to perovskite oxides, the cation-octahedra of Mn3GaN are resilient to strain and the system prefers to adjust into a centrosymmetric tetragonal structure. In order to understand this resilience, the implications of the intermetallic nature of antiperovskites are addressed, and a detailed mapping of how the chemical bonds are affected by strain in Mn3GaN is compared to the effect of strain on the ionic bonds in the canonical cubic oxide perovskite SrTiO3. The stiffness of the Mn3GaN phonon structure to strain will also be compared to phonon modes that cause octahedral rotations in perovskites. Lastly, the effect of biaxial strain of Mn3GaN on electronic properties will be addressed via band structure investigations.