The surface electronic properties of newly designed half-metallic ferromagnets: GeKCa and SnKCa

• Surface properties of half-Heusler alloys, CaKCa and SnKCa, are studied.
• Two possible terminations of (0 0 1) surface are considered.
• Ge and Sn terminated surfaces retain the half-metallic properties of the bulk.
• KCa terminated surfaces exhibit metallic character and are strongly demagnetized.
• Magnetic properties of the halfmetallic surfaces are enhanced compared with the bulk.

The electronic and the magnetic properties of the (0 0 1) surfaces of GeKCa and SnKCa with half-Heusler structure are studied with the use of a full-potential linearized augmented plane wave method. It is shown that although the two compounds are half-metals in their bulk structures, only the surfaces terminated with a carbon group atom retain the half-metallic properties. The magnetic properties of the surfaces terminated with layers containing group 14 atoms are enhanced compared with the properties of the bulk. The calculated magnetic moments on the Ge atom in GeKCa are 0.38μB in the bulk and 0.97μB at the (0 0 1) surface. In the SnKCa surface, the value of the magnetic moment on the Sn atom increases from 0.28μB in the bulk to 0.75μB at the surface. In the Ge (Sn) terminated Ge(Sn)KCa surfaces, the metal atoms are also polarized. In addition to destroyed half-metallicity at the surfaces terminated with metal atoms we also find a strong demagnetization of the systems.