  Motivated by the recently synthesized nanoparticle size Co3Si P63/mmc which
displays remarkable magnetic property [Appl. Phys. Lett. 108, 152406 (2016)],
we thus searched cobalt silicides and several useful phases have been searched
including a structure Cmcm with 60 meV/atom lower than that of P63/mmc. A
lower-energy Co phase is predicted, (-7.03 eV/atom), whose energy is higher
than that of P63/mmc (-7.04 eV/atom) but is lower than that of (-7.02 eV/atom).
Three low-energy Fe5Si3 structures are searched, all of them are about 30
meV/atom lower than the experimental P63/mcm and present small magnetism.
Meanwhile, the strong lattice shape dependence of magnetocrystalline anisotropy
energy (MAE) is studied through X5Si3 (X=Mn, Fe, Co). Our extensive analysis
observed that the building-block shape of cobalt silicide is generally same and
is dominated by the Co P63/mmc, Fm-3M, R-3m, and their energy order also
depends on the energy order of the several Co building blocks. All of the
searched Co3C and Co3Sn have positive formation of energy, thus only Co3Ge has
similar low-energy structures with those of Co3Si. Several low-energy perfect
or nearly-perfect easy-axis/plane MAE Mn3Si, Mn5Si2, and Mn5Si3 structures are
also searched and present very important application, the similar structure and
MAE also exist in Ge-containing counterparts. A structure I4122 with energy
about 300 meV/atom lower than that of experimental Mn5Si3 P63/mcm is searched.
All of the above mentioned structures are about 100 meV/atom lower than that of
the searched lowest-energy structure or experimental structure.
