Ferrimagnetism and disorder of epitaxial Mn_2−xCo_xVAl Heusler compound thin films

Abstract

The quaternary full Heusler compound Mn 2− x Co x VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0–2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn 2 VAl ( x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpreted with the help of band structure calculations in the coherent potential approximation. Mn 2 VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co 2 VAl has B2 order and has reduced magnetization. In the cases with x ⩾ 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.