Electronic and Magnetic Properties of X2Mn1-xVxSi (X=Fe and Co)

We have performed energy-band calculations of X 2 Mn 1- x V x Si (X=Fe and Co) at x =0, 0.25, 0.5, 0.75, 1.0. In ferromagnetic ordering, we obtain excellent agreement between calculated and experimental data for the magnetic moment per formula unit and the lattice constant, at each Mn content. We have obtained the result that state densities in Fe 2 Mn 1- x V x Si have a large peak at the Fermi level, while they do not in Co 2 Mn 1- x V x Si. We have also estimated Heisenberg exchange constants from total energy differences between ferromagnetic and antiferromagnetic orderings. The Curie temperature roughly calculated from the exchange constants increases from x =0 to x =0.5 and then decreases rapidly in Fe 2 Mn 1- x V x Si, though it monotonically decreases from x =0 to x =0.75 in Co 2 Mn 1- x V x Si. The behavior of calculated Curie temperatures in Fe 2 Mn 1- x V x Si is consistent with the observed one.