Competing magnetic phases of Mn5Ge3 compound

Germanium-based compounds have recently attracted considerable attention in Semiconductor Spintronics. The Mn5Ge3 compound have been grown on Ge(111) substrate so that epitaxial 'spin valves' can be fabricated. Recent experiments suggest a spin structure that is likely non-collinear. In order to gain deep insights into the magnetic structure of this compound, we have performed fully unconstrained ab-initio pseudo-potential calculations within spin density functional theory. We have considered several possible magnetic configurations: paramagnetic (PM), collinear (C) ferromagnetic (FM) and anti-ferromagnetic (AFM), non-collinear (NC) spin configurations. We first study the effect of the pressure. At equilibrium volume (V-eq = 0.203 nm(3)), the C-FM and NC self-consistent solutions (which have different magnetic states) are competing phases. For V similar or equal to 1.1 V-eq there is a crossover of the C-FM and C-ATM curves, with the C-AFM becoming favourite with respect to C-FM for larger volumes. Finally, we have studied the effect of strain field. Interestingly, the degeneracy of the NC phase with the C-spin configurations (FM and AFM) is definitely removed under the effect of uniaxial structural distortions (NC spin configuration is favoured under tensile uniaxial strain).