Structural stability, electronic, magnetic and thermoelectric properties for half-metallic quaternary Heusler alloys CrLaCoZ

Abstract

Using first-principles calculations, we predict the CrLaCoZ (Z = Al, Ga, In, Ge, Sn, Pb) Heusler alloys to be half-metals, and their total magnetic moments follow the Slater-Pauling rule Mt = Zt − 18. Structural stability is estimated in terms of thermodynamics, dynamic, mechanical and thermal. A comparison in total energy shows that the CrLaCoZ alloys have ferrimagnetic ground states, and the competition between d-d exchange, super-exchange and RKKY exchange interactions leads to the appearance of magnetic order phase. Phase separation shows that CrLaCoAl, CrLaCoGa, CrLaCoIn and CrLaCoSn are easier to be synthesized in experiment. The formation of half-metallic gap ascribes to the d-d, p-d orbital hybridizations. Furthermore, we find that the magnitude of gap is decided by the strength of exchange splitting between eg and t2g states according the distribution and occupation of electronic states. Presence of X and DO3 disorders destroys their half-metallicity. In addition, we examine the effects of spin-orbit coupling on electronic structure, and calculate their thermoelectric properties by using Boltzmann transport theory. From the calculated exchange interactions, it is found that the Cr(A)-Cr(A), Cr(A)-La(B) and Cr(A)-Co(C) exchanges play a leading role in all interactions, and finally determine the Curie temperatures. Apart from the CrLaCoSn alloy, other alloys have evidently higher Curie temperatures than room temperature, which is favorable as an electrode materials in magnetic tunnel junction.