Bulk and surface DFT investigations of the electronic and magnetic properties of CsXNO (X = Mg, Ca and Sr) quaternary Heusler alloys

The structural, electronic and magnetic properties of the bulk and (001) surfaces of CsXNO (X = Mg, Ca and Sr) quaternary Heusler alloys are investigated. It is found that all of the compounds are half-metallic ferromagnets with a magnetic moment of 2 mu(B) which obeys the Slater-Pauling rule. The half-metallic gaps are calculated to be 0.84, 0.80 and 0.82eV for CsMgNO, CsCaNO and CsSrNO, respectively. It seems that the shift of the bands due to the rather strong p-p exchange interaction leads to half-metallic ferromagnetism in these compounds. They can also maintain their half-metallic properties under great stresses and the calculated Curie temperatures are 705.14, 504.85 and 488.82 K for CsMgNO, CsCaNO and CsSrNO, respectively. The (001) surfaces of the compounds are also simulated using the symmetric slab model. The results of the calculation of surface energies indicate that NO-terminated surface is more stable than CsX-terminated surface. The half-metallicity is also well preserved on the NO-terminated surface, however the bulk half-metallicity is destroyed by the surface states on the CsX-terminated slab. Considering the 100 % ferromagnetic spin polarization in bulk and surface beside high Curie temperature make these materials excellent candidates for spintronic applications.