Half-metallicity and magnetism of CoFeHfGe novel quaternary Heusler alloy in bulk form as well as (100) and (001) surfaces: An ab initio study

In this study, we investigated the electronic and magnetic nature of the LiMgPdSn-type CoFeHfGe quaternary Heusler alloy in the bulk form as well as the (100) and (001) surfaces using density functional theory within the generalized gradient approximation scheme. The bulk CoFeHfGe alloy was predicted to exhibit half-metallic behavior with an electronic band gap of 0.37 eV and 100% spin-polarization at an equilibrium lattice parameter of 6.08 Å. The elastic constants and phonon dispersion confirmed the mechanical and dynamical stability of the bulk form considered. The total magnetic moment was determined as 1μ_B/f.u. for the CoFeHfGe alloy. The atomic relaxation and surface energy were investigated for the (100) and (001) surfaces of the CoFeHfGe alloy, and the results indicated that the slabs are stable, where CoFe (001) has the lowest surface energy among all of the terminations. For (100) and (001) slabs of the CoFeHfGe alloy, we found that the half-metallicity is destroyed due to the surface states and the HfGe (100) slab has the highest spin polarization of 90.72%, and thus it can be used in giant magnetoresistance devices. The magnetic moments in the layers of the HfGe (100) slabs are similar to the corresponding bulk and magnetic moments of the surface atoms, where they tend to increase with depth in the CoFe (100) slab.