First-principles study on electronic structure, magnetism and half-metallicity of the NbCoCrAl and NbRhCrAl compounds

Abstract

The electronic structure, magnetism and half-metallicity of quaternary Heusler compounds NbCoCrAl and NbRhCrAl were investigated theoretically by using first-principles calculations. It was found that the equilibrium lattice constants of NbCoCrAl and NbRhCrAl compounds are 6.02 Å and 6.18 Å, respectively. The total magnetic moment is 1 μB and consistent with the Slater-Pauling formula: Mt = 24 − Zt. The half-metallicity can be kept when the lattice constant changes in the range of 5.87–6.07 Å and 5.954–6.279 Å for NbCoCrAl and NbRhCrAl compounds, respectively. The half-metallic band gap locates between the eu and t1u states originating from the hybridizations of the d states of Cr and Co (Rh) atoms. Compared with NbCoCrAl, as the radius of Rh with valance electron in 4d states is bigger than that of Co with valance electron in 3d states, NbRhCrAl has a more stable half-metallicity and bigger equilibrium lattice constant. In particular, the half-metallicity of NbRhCrAl is more robust against the lattice thermal expansion with increasing temperature. Keywords: Half-metallicity, Heusler compounds, First-principles calculations, Lattice thermal expansion