Title: Structures, phase transitions, and magnetic properties of Co3Si from first-principles calculations,
Abstract: Co3Si was recently reported to exhibit remarkable magnetic properties in the
nanoparticle form [Appl. Phys. Lett. 108, 152406 (2016)], yet better
understanding of this material is to be promoted. Here we report a study on the
crystal structures of Co3Si using adaptive genetic algorithm, and discuss its
electronic and magnetic properties from first-principles calculations. Several
competing phases of Co3Si have been revealed from our calculations. We show
that the hexagonal Co3Si structure reported in experiments has lower energy in
non-magnetic state than ferromagnetic state at zero temperature. The
ferromagnetic state of the hexagonal structure is dynamically unstable with
imaginary phonon modes and transforms to a new orthorhombic structure, which is
confirmed by our structure searches to have the lowest energy for both Co3Si
and Co3Ge. Magnetic properties of the experimental hexagonal structure and the
lowest-energy structures obtained from our structure searches are investigated
in detail.