Stable half-metallicity in the (001)-oriented thin films of Co-doped full-Heusler alloys TiFeCoSn (=0.00, 0.25, 0.50, 0.75 or 1.00).

Thin films with stable half-metallic (HM) character and 100% spin-polarization (SP) are required to be used in spintronic devices. The HM character has been predicted theoretically in many Heusler alloys thin films and confirmed by experiments. Full-Heusler alloy TiFeSn has been studied extensively. It has been reported that their (001)-oriented thin films with TiFe or TiSn terminations preserve 100% SP, but the HM character is unstable because the edge of the bandgap is closed to the Fermi level. Therefore, we investigate the effects of the Co-doping on the structural, electronic and magnetic properties of the bulk full-Heusler alloys TiFeCoSn (= 0.00, 0.25, 0.50, 0.75 or 1.00) and their (001)-oriented thin films. The bulk TiFeCoSn (= 0.00, 0.25, 0.50, 0.75 or 1.00) alloys are all HM ferromagnets. We investigate twelve possible terminations and show that five of them preserve HM character with 100% SP at the Fermi level, while in the remaining seven, surface states emerge in the spin-down channel at the Fermi level, significantly reducing their SP. The Co-doping significantly increases the stability of the TiSn slab, also increases its spin-down bandgapEg↓and HM gapEgHMat= 0.50. The stable HM character makes it is a slab of maximum benefit in the applications of spintronic devices, especially in magnetic tunnel junctions.