Theoretical study of surface properties of new (0 0 1)- and (1 1 1)-surface YCoCrGe quaternary Heusler compounds

Highlights: • Half-metallic Heusler alloys have promising applications in spintronic systems. • Half metallicity is destroyed in the Y-Ge and Cr-Co for the (001) surface. • Half-metallicity is confirmed in the Cr- (111)surface with full spin polarisation. - Abstract: Studies have shown that the YCoCrGe quaternary Heusler compound exhibits half-metallic properties. We predicted the electronic and magnetic properties for the (0 0 1)- and (1 1 1)-surface YCoCrGe quaternary Heusler compounds with LiMgPdSn–type structure based on the computation of first principles. We analysed the effects of the surface and correlation interactions on the electronic and magnetic properties and thus the half-metallicity and the spin polarisation of the bulk and surfaces (0 0 1) and (1 1 1) YCoCrGe quaternary Heusler alloys, with two ideal surfaces named Y-Ge and Cr-Co for the (0 0 1) surface and four ideal surfaces named Y, Co, Cr, and Ge for the (1 1 1) YCoCrGe. We observed that the half-metallicity confirmed in the YCoCrGe bulk system fails to appear on all surfaces other than the Cr-termination, with spin polarisation at about 64% and 76% for Y-Ge and Cr-Co respectively, and 70%, 51%, and 68% for the Y, Co, and Ge surfaces respectively. In the Cr-terminated surface, we observed that half-metallicity is confirmed with spin polarisation equal to 100%, and that the magnetic moment calculated was found to be equal to an integer value. In the (0 0 1) and (1 1 1) surfaces, the calculation of the magnetic moment for Co and Cr atoms (except for the Y-termination, where the Co atom increased to 1.04 μᵦ) was found to have decreased to that of the bulk system. These calculations indicate that the YCoCrGe quaternary Heusler compound is promising for applications of spintronic systems.