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First-principles study of the (001) and (110) surfaces of CrCoIrGa Heusler alloy

Exploring highly spin-polarized thin films of magnetic materials is of great importance for spin-based device applications. Herein, the structure, spin-polarization and magnetic properties of the (001) and (110) surfaces of CrCoIrGa Heusler alloy have been investigated using first-principles density functional theory (DFT) and DFT + U calculations. The results demonstrate that while bulk CrCoIrGa is highly spin-polarized (89%), the surface counterparts exhibit much lower spin-polarization (SP), being due to the emergence of surface states at Fermi level (EF). It is observed that the (001) surface geometries are kept well, whereas, the (110) surface exhibit an obvious surface reconstruction after relaxation, resulting in large surface formation energy. The electronic properties investigated at DFT level revealed that CrGa-terminated (001) surface carries 100% SP, CoIr-terminated has 63% SP, and the (110) surface retains the bulk SP. Interestingly, the SP is found to be suppressed on introducing U parameter in the calculations. All the considered surfaces display ferrimagnetic coupling, with a significant total magnetic moment. In addition, the surface layer atoms carry large SP and moments than the inner layer atoms, and thus promise a dominant role in spin-based device applications of the thin film surfaces.