Anomalous transport and metal to half-metal evolution induced by Cr doping in Co2FeGa

This paper aims to enhance the spin polarization of the Heusler alloy Co2FeGa by replacing Co with Cr. It is found that, as the substitution content x increases from 0 1 2 in Co2-xCrxFeGa alloys, the Fermi level in the spin-up direction is tuned from the low density of states (DOS) of hybridized orbital t2g to the small pseudogap between eg and t1u and finally to the area of high DOS formed by the antibonding t1u and eu hybridized orbitals. Meanwhile, the Fermi level of the spin-down direction remains in the pseudogap. Hence a transition from a ferromagnetic metal (x = 0) to a ferrimagnetic (FIM) spin-gapless semiconductor (SGS; x = 1) and further to a FIM near half-metal (HM) (x = 2) was realized with the spin polarization enhanced from 63% to 95%. Furthermore, the disorder between Cr(B) and Ga does not destroy the HM property of Cr2FeGa. Theoretically, the intrinsic anomalous Hall conductivity induced by the Berry curvature is found to increase with doping Cr in ordered Co2-xCrxFeGa. Experimentally, the saturation magnetic moments of Co2FeGa and CoCrFeGa were measured to be 5.21 mu B/f.u. and 2.25 mu B/f.u. at 5 K, respectively, which is consistent with first-principles calculations. However, in Cr2FeGa, there is an obvious deviation between the experimental value of 0.36 mu B/f.u. at 5 K and the calculated value of 0.96 mu B/f.u., which is attributed to the swap disorder in the sample. The longitudinal resistivity shows Co2FeGa a metallic conductor behavior, whereas both CoCrFeGa and Cr2FeGa exhibit semiconductorlike behavior from 5 to 350 K. In the compound CoCrFeGa, the small anomalous Hall conductivity (sigma xAy) of 52.7 S/cm at 5 K is in line with the property of SGS. Both intrinsic and extrinsic factors contribute to the anomalous Hall effect in CoCrFeGa, with the intrinsic contribution being larger than that of the extrinsic part. For Cr2FeGa, a maximum of the value of sigma xAy 14.1 S/cm is observed at 5 K, and this value goes to zero above 150 K due to Curie transition.