Mn₅Ge₃ thin films epitaxially grown on Ge(111) exhibit metallic conductivity and strong ferromagnetism up to about 300 K. Recent experiments suggest a non-collinear 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 Non-Collinear (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 occurence of accidental magnetic degeneracy also in Mn₅Ge₃ real samples. We found a continuos transition from a ferromagnetic C low-spin state at small volums 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.

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