Non-collinear magnetic states of Mn5Ge3 compound

Mn5Ge3 thin films epitaxially grown on Ge(1 1 1) exhibit metallic conductivity and strong ferromagnetism up to about 300 K. Recent experiments suggest a non-collinear (NC) spin structure. In order to gain deep insights into the magnetic structure of this compound, we have performed fully unconstrained ab initio pseudopotential calculations within density functional theory, investigating the different magnetic states corresponding to collinear (C) and NC spin configurations. We focus on their relative stability under pressure and strain field. Under pressure, the C and NC configurations are degenerate, suggesting the possible occurrence of accidental magnetic degeneracy also in Mn5Ge3 real samples. We found a continuous transition from a ferromagnetic C low-spin state at small volumes to a NC high-spin state at higher volumes. Remarkably, the degeneracy is definitely removed under the effect of uniaxial strain: in particular, NC spin configuration is favoured under tensile uniaxial strain.