Effects of thermal spin disorder on the half-metallicity of Co₂MnSi with antisite defects and Fe substitution

Heusler alloys based on Co₂MnSi have a high Curie temperature and high spin polarization at the Fermi level, which is promising for applications in spintronics. Band structure calculations show Co₂MnSi to be half-metallic at zero temperature. Alloying with Fe on the Mn sublattice is believed to shift the Fermi level closer to the middle of the half-metallic gap. Here, we study the effects of thermal spin fluctuations on the electronic spectrum near the Fermi level, both in pure Co₂MnSi and in the presence of crystallographic defects or Fe substitution for Mn.We find that all magnetic antisite defects are strongly exchange-coupled to the host magnetization, and thermal spin fluctuations do not easily destroy the half-metallic gap. In this respect, Co₂MnSi differs from NiMnSb, where Mn antisites on the Sb sublattice strongly reduce the spin polarization already at rather low temperatures [1]. We also find that partial substitution of Mn by Fe results in considerable changes in the Bloch spectral function near the Fermi level, which are very different from the rigid-band picture that is usually assumed.
[1] K. D. Belashchenko, J. Weerasinghe, S. Mu, and B. S. Pujari, Phys. Rev. B 91, 180408(R) (2015).