Bandgap engineering of the (001) oriented thin-films of the Heusler alloys Co2‒xFexCrAl (x=0.00, 0.25, 0.50, 0.75 or 1.00)

Abstract

Materials which possess 100% spin-polarization (SP) at their thin-film form are essential for spintronic devices. The half-metallicity has been predicted theoretically in many Co-based Heusler alloys thin-films. Especially the Heusler alloy Co2CrAl has been studied extensively. A previous study reported that the CrAl terminated (001) oriented thin-film had 84% SP, while the other study reported that the CrAl terminated (001) oriented thin-film had 100% SP. Therefore, we investigate in detail the effects of the Fe-doping on the structural, electronic and magnetic properties of the bulk Heusler alloys Co2‒xFexCrAl (x=0.00, 0.25, 0.50, 0.75 or 1.00) and their various terminated (001) oriented thin-films. All the bulk Heusler alloys Co2‒xFexCrAl and their x-CrAl terminated (001) oriented thin-films possess half-metallicity and 100% SP at the Fermi level EF. The surface energy Es of the x-CrAl terminated (001) oriented thin-films increases with Fe-doping concentration x. The CrAl terminated (001) oriented thin-films of the Heusler alloys Co2‒xFexCrAl (x=0.00, 0.25, 0.50, 0.75 or 1.00) maintain the half-metallic (HM) character and 100% SP and thus can be used in spintronic devices, especially the 0.50-CrAl terminated (001) oriented thin-film with the largest spin-down bandgap Eg↓ of 0.213 eV and the largest HM bandgap EgHM of 0.106 eV.