Spin-gapless semiconducting nature of Co-rich Co1+xFe1-xCrGa

Spin gapless semiconductors (SGSs) are an interesting class of materials which bridge the gap between semiconductors and half-metallic ferromagnets. This class of materials shows band gap in one of the spin channels and a zero band gap in the other, and thus promote tunable spin transport. Here, we present structural, electronic, magnetic, and transport properties of Co-rich SGS Co1+xFe1-xCrGa using both theoretical and experimental techniques. The key advantage of Co-rich samples Co1+xFe1-xCrGa is the high Curie temperature (T-C) and magnetization, without compromising the SGS nature (up to x = 0.4), and hence our choice. The quaternary Heusler alloys Co1+xFe1-xCrGa (x = 0.1 to 0.5) are found to crystallize in LiMgPdSn-type structures having space group F (4) over bar 3m (number of 216). The measured Curie temperature increases from 690 K (x = 0) to 870 K (x = 0.5). The obtained T-C for x = 0.3 (790 K) is found to be the highest among all previously reported SGS materials. Observed magnetization values follow the Slater-Pauling rule. Measured electrical resistivity, in the temperature range of 5-350 K, suggests that the alloys retain the SGS behavior up to x = 0.4, beyond which it reflects metallic character. Unlike conventional semiconductors, the conductivity value (sigma(xx)) at 300 K lies in the range of 2289 S cm(-1) to 3294 S cm(-1), which is close to that of other reported SGS materials. The anomalous Hall effect is comparatively low. The intrinsic contribution to the anomalous Hall conductivity increases with x, which can be correlated with the enhancement in chemical order. The anomalous Hall coefficient is found to increase from 38 S/cm for x = 0.1 to 43 S/cm for 0.3. Seebeck coefficients turn out to be vanishingly small below 300 K, another signature for being SGS. All the alloys (for different x) are found to be both chemically and thermally stable. Simulated magnetization agrees fairly with the experiment. As such, Co-rich CoFeCrGa is a promising candidate for room temperature spintronic applications, with enhanced T-C, magnetic properties, and SGS nature.