Half-metallicity and magnetism of Heusler alloys Co₂HfZ (Z = Al, Ga, Ge, Sn)

Highlights: • The Cu₂MnAl-type structure is more stable than the Hg₂CuTi-type structure for Co₂HfZ alloys. • The Cu₂MnAl-type structures of Co₂HfZ exhibit half-metallic ferrimagnetic behavior. • The total magnetic moments of the Cu₂MnAl-type Co₂HfZ obey the Slater–Pauling rule (M_tot = Z_tot − 24). - Abstract: The electronic and magnetic properties of novel Heusler alloys Co₂HfZ (Z = Al, Ga, Ge, Sn) with Hg₂CuTi- and Cu₂MnAl-type structures are investigated by first-principles calculations. It is found that the Cu₂MnAl-type structure is more stable than the Hg₂CuTi-type structure for all the Co₂HfZ alloys. The Hg₂CuTi-type structures of Co₂HfZ show a metallic ferrimagnetic character with a high spin polarization. The Cu₂MnAl-type structures have half-metallic ferrimagnetic behavior with minority-spin gaps of 0.38, 0.06, 0.55 and 0.46 eV for Co₂HfAl, Co₂HfGa, Co₂HfGe and Co₂HfSn, respectively. The total magnetic moments of the Cu₂MnAl-type alloys are 1µ_B, 1µ_B, 2µ_B and 2µ_B, which obey the Slater–Pauling rule (M_tot = Z_tot − 24). Analysis of the projected density of states indicates clear gaps resulting from the hybridization of Co (A) and Co (B) atoms. The half-metallicity makes Co₂HfZ with Cu₂MnAl-type structure promising candidates for spintronic applications.