Suppression of Co-Cr antisite defect and robust half metallicity in CoMCrAl (M = Mn, Fe) Heusler alloys

Quaternary alloys CoMnCrAl, CoFeCrAl and their ternary counterpart Co2CrAl are studied experimentally and theoretically to explore the effects of the substitution of Mn or Fe atoms for part of Co atoms in Co2CrAl. It is found that CoMnCrAl or CoFeCrAl has a magnetization 0.92 mu(B)/f.u. or 1.96 mu(B)/f.u. respectively in agreement with the Slater-Pauling (SP) rule, different from the parent ternary alloy Co2CrAl whose magnetization significantly deviates. The combination of experimental and theoretical results suggests that the formation of Co-Cr antisite defect is suppressed by partially substituting Mn or Fe for Co. The main disorder defects in CoMnCrAl are Cr-Al and Mn-Cr antisites, Fe-Cr and Cr-Al antisites in CoMnCrAl. Since these antisite defects only have small effect on the minority band structure, the half metallicity of CoMnCrAl or CoFeCrAl is expected to have much better tolerance for atomic disorder, compared with Co2CrAl. A negative temperature coefficient of resistance for a long temperature range about 10-273 K has been found exclusively for CoMnCrAl compound. Quaternary alloy CoMnCrAl or CoFeCrAl is found to be compensated ferrimagnetism with a relative low magnetization but a Curie temperature (T-C) significantly higher room temperature (RT), whose magnetization are relatively low, but T-C higher than the ternary alloy Co2CrAl. Considering their low magnetization, decently high T-C and the robust half metallicity, these two quaternary alloys may have important applications in spintronic devices. (C) 2021 Published by Elsevier B.V.