Ab initio study of disorder effects on the electronic and magnetic properties in quaternary Heusler alloys

Abstract

First-principles calculations, combined with the supercell approach, are employed to investigate the effects of atomic disorder on the electronic and magnetic properties of the CoFeMnZ (Z = Ge or Al) equiatomic quaternary Heusler alloy (LiMgPdSn-type). The ordered CoFeMnGe alloy is a nearly-half-metallic ferromagnet and can be transformed into full half-metal at 28.35 GPa of pressure. The ideal CoFeMnAl is half-metallic; Both compounds follow the Slater-Pauling rule with Curie temperature TC above 300 K. We analysed twelve antisite and six swap disorder configurations. For CoFeMnGe Calculations show that the FeGe antisite is the most energetically favourable defect (-9.95 eV), followed by the FeMn, CoGe and CoMn antisite structures. Half-metallicity is completely lost for CoGe, GeFe antisite and CoGe, FeGe swap defects. GeCo and MnGe antisite, FeGe and MnGe swap enhance half-metallicity by pushing the VBM below the Fermi level. The FeMn antisite gives 4.135 μB/f.u, which is very close to the experimental value of 4.2 μB. For CoFeMnAl Calculations show that the FeMn antisite is the most energetically favourable defect (-1.25 eV), followed by the FeCo antisite and the MnAl swap. The disorder generally contracts the spin-down gap. Half-metallicity is largely preserved but completely lost for CoAl, CoMn antisite and CoAl, CoMn swap defects. The FeMn antisite gives 3.12 μB, which is very close to the experimental value of 3.10 μB. Disorder has a significant effect on the magnetic moment and Curie temperature for both compounds. This study demonstrates the importance of considering disorder when predicting the properties of Heusler alloys.