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

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 1µB, 1µB, 2µB and 2µB, which obey the Slater-Pauling rule (Mtot = Ztot − 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.