Half-metallicity of the bulk and (001) surface of NbFeCrAl and NbFeVGe Heusler compounds: a first-principles prediction

Using first-principles calculations based on density-functional theory, the structural, electronic and magnetic properties in the bulk and (001) surfaces of quaternary Heusler compounds NbFeCrAl and NbFeVGe are investigated. For the bulk, the two compounds exhibit half-metallicity with band gaps of 0.4 eV and 0.2 eV in the majority-spin direction at their equilibrium lattice constants. The total magnetic moments are 2 mu(B) following the Slater-Pauling formula: M-t = 24 - Z(t) rule. The half-metallicity can be maintained in the range of 5.76-6.07 angstrom and 5.96-6.10 angstrom (lattice constant), and 0.971-1.035 and 0.962-1.033 (c/a) for NbFeCrAl and NbFeVGe compounds, respectively. The half-metallicity is destroyed on the Fe-Cr, Nb-Al, Fe-V, and Nb-Ge terminated (001) surfaces, and the spin-polarization ratio sharply decreases below 50% for NbFeCrAl and NbFeVGe compounds.