Origin of spin gapless semiconductor behavior in CoFeCrGa: Theory and Experiment

Abstract

Despite a plethora of materials suggested for spintronic applications, a new class of materials has emerged, namely spin gapless semiconductors (SGS) that offers potentially more advantageous properties than existing ones. These magnetic semiconductors exhibit a finite band gap for one spin channel and a closed gap for the other. Here, supported by electronicstructure calculations, we report the first experimental evidence of SGS behavior in equiatomic quaternary CoFeCrGa, having a cubic Heusler (prototype LiMgPdSn) structure but exhibiting chemical disorder (DO 3 structure). CoFeCrGa is found to transform from SGS to half-metallic phase under pressure, which is attributed to unique electronic-structure features. The saturation magnetization (M S ) obtained at 8 K agrees with the Slater-Pauling rule and the Curie temperature (T C ) is found to exceed 400 K. Carrier concentration (up to 250 K) and electrical conductivity are observed to be nearly temperature independent, prerequisites for SGS. The anomalous Hall coefficient is estimated to be 185 S/cm at 5 K.Considering the SGS properties and high T C , this material appears to be promising for spintronic applications.

Equiatomic quaternary Heusler alloys: A material perspective for spintronic applications

“…Bainsla et al [10], also performed ab-initio calculations to get better insight into the magnetic behavior of CoFeCrGa alloy. As per these calculations, the total magnetic moment 14 was found to be constant as a function of lattice parameter, which supports their experimental claims.…”

“…To further investigate the crystal structure of CoFeCrGa, Bainsla et al [10] performed room temperature 57 Fe Mössbauer spectroscopic measurements. Mössbauer spectrum was best fitted with two sextets having hyperfine field values of 254 and 142 kOe and relative intensities of 58, 34 respectively, along with a doublet of 8% intensity (paramagnetic).…”

“…Bainsla et al [10], studied the magnetic properties of CoFeCrGa alloy by recording the thermomagnetic curves in the temperature range of 5-400 K with applied magnetic field of 500 Oe. Curie temperature value is expected to be more than 400 K as no magnetic transitions were observed in the thermomagnetic curves up to that temperature.…”

“…But, such a behavior is confirmed experimentally only in a few of them. i.e., Mn2CoAl [26], CoFeMnSi [8] and CoFeCrGa [10]. Very recently, thin films of Mn2CoAl were synthesized to check its applicability in the devices [33,34].…”

“…Since, the prediction of HMF nature in NiMnSb [6], Heusler alloys have received a special attention due to the reasons mentioned above. In the large family of Heusler alloys, generally Co based alloys show relatively high Curie temperature and high spin polarization [7][8][9][10][11][12][13][14][15][16].…”