Half-metallicity in CrAl-terminated CoCrAl thin film.

Half-metals with high Curie temperature are ideal candidates for applications in spin-based electronics-an emerging technology utilizing a spin degree of freedom in electronic devices. Many half-metallic materials have been predicted theoretically, and some have been confirmed experimentally. At the same time, in thin-film geometry the electronic structure of these materials may change due to the potential presence of surface/interface states. This could limit practical applications of these materials in nano-size devices, since typically these states result in reduced spin-polarization. Here, from first principles we study a full Heusler compound, CoCrAl in thin film geometry. This material has been studied extensively, and it has been reported that it exhibits half-metallic properties in the bulk. We show contrary to the earlier reports that this material retains 100% spin polarization in CrAl-terminated thin film geometry (Co-termination results in destroyed half-metallicity). Moreover, we confirm that under biaxial strain CoCrAl retains half-metallicity for a practically feasible range of considered pressure, i.e. in principle it may stay half-metallic if used in thin-film heterostructures, where lattice mismatch is a common scenario. The magnetic alignment of CoCrAl is confirmed to be ferromagnetic, with the non-integer total magnetic moment of Co-terminated cell, and the integer total magnetic moment of CrAl-terminated cell, consistent with their corresponding non-half-metallic and half-metallic electronic structures. If confirmed experimentally, these results may have an important impact in spin-based electronics.