First-principles study on the magnetic and half-metallic properties in bulk and (001) surface of Ti2CoSn Heusler alloy

• Bulk Ti2CoSn is spin-gapless semiconductor (SGS) ferromagnetism with 3 μB/f.u. moment.
• All terminations of the (001) surface of the Ti2CoSn alloy lose the SGS character.
• Atomic magnetic moments at the (001) surface are greatly different from the bulk values.

For the bulk and (001) surface of Ti2CoSn Heusler alloy, the electronic and magnetic properties in bulk and the surface effect on the structural, electronic and magnetic properties of the alloy for different terminations of (001) surface have been studied by using first-principles calculations. The spin-gapless semiconductor (SGS) ferromagnetism with the magnetic moment of 3.00 μB/f.u. is confirmed in the bulk Ti2CoSn alloy with Hg2CuTi-type structure. For two ideal terminations (TiCo, TiSn) and three modified terminations (CoCo*, TiTi*, SnSn*), the density of states (DOS) indicates that all terminations destroy the SGS character. Furthermore, we find that the atomic magnetic moments (AMM) decrease for the most atoms on the outmost three layers due to structural relaxation of these atoms inward. Both the DOS and AMM of the central layer L9 are similar to the corresponding bulk characters because surface effects fade out at the position of the inner layer, 12 Å below the surface.