Ferrimagnetism and disorder in epitaxial Mn(2-x)Co(x)VAl thin films

TL;DR

This study investigates the magnetic properties and disorder effects in epitaxial Mn(2-x)Co(x)VAl thin films, revealing ferrimagnetic coupling, sensitivity to disorder, and the transition to ferromagnetism with increasing Co content.

Contribution

It provides new experimental insights into the magnetic structure and disorder effects in Mn-Co-V-Al thin films, supported by band structure calculations.

Findings

Ferrimagnetic coupling observed in Mn2VAl and Mn-Co-V-Al films.

Magnetic moments are reduced due to disorder and band structure effects.

Transition to ferromagnetism occurs at Co content x >= 0.9.

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 (001) 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 Mn2VAl (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. Mn2VAl is very sensitive to disorder involving Mn, because nearest-neighbor Mn atoms couple anti-ferromagnetically. Co2VAl 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.