First-principles study of the Co2FeSi(001) surface and Co2FeSi/GaAs(001) interface

Ab initio study of the electronic and magnetic properties of bulk Co2FeSi, free Co2FeSi(001) surfaces, and its interfaces with GaAs (001) substrate are reported. The bulk computations indicate that the LSDA+U scheme is necessary to reproduce the measured total magnetic moments and to observe a half-metallic behavior. The thermodynamic stability of various Co2FeSi(001) surface and Co2FeSi/GaAs(001) interface terminations are studied in the framework of ab initio thermodynamics. The calculated surface phase diagram indicates that by tuning the atomic chemical potentials, three different terminations are probable. The obtained interface diagrams argue the possibility of the formation of mixed interfaces. The spin-polarized density of states shows that the half metallicity confirmed in the bulk Co2FeSi is lost at its surfaces and interfaces with GaAs(001).