Structural disorder and short-range order in full Heusler alloys Fe2VAl and Co2CrAl from first principles calculations

Heusler alloys are intensively studied and applied in various spintronic devices. First principles calculations of their electronic structure allow to predict promising compounds with high spin polarization. However the theoretical predictions usually substantially deviate from experimental data. One of the reason is incorrect structural models used in the calculations. Heusler alloys are apt to form various disordered modifications with high concentration of antisite defects. In this paper we considered the effects of structural order and disorder on the electronic structure, stability and magnetic properties of full Heusler alloys Fe2VAl and Co2CrAl. The ordered Fe2VAl is non-magnetic narrow-gap semiconductor, the ordered Co2CrAl is a ferromagnet with metal behavior for majority spin band and narrow-gap semiconductor for minority one. When disordering Fe2VAl becomes a ferromagnetic metal. Co2CrAl loses minority band gap and its spontaneous magnetization reduces by 32%. Introduction of short range order in the disordered structure by increasing the portion of clusters specific for bcc structure further raised the magnetization in Fe2VAl and did not change it in Co2CrAl.