Effects of disorder on the magnetic properties of the Heusler alloy V$_{2}$FeAl

TL;DR

This study investigates how atomic disorder affects the magnetic properties of V$_{2}$FeAl Heusler alloys, revealing that increased disorder reduces magnetic moments and Curie temperature, with differences between bulk and thin-film samples.

Contribution

It provides a comparative analysis of magnetic properties in bulk and thin-film V$_{2}$FeAl, highlighting the impact of atomic ordering and disorder on magnetism through experimental and computational methods.

Findings

Thin films show higher atomic order and ferrimagnetism.

Disorder reduces magnetic moments and Curie temperature.

Bulk alloy is a Pauli paramagnet with no spontaneous magnetization.

Abstract

Magnetic properties of multicomponent alloys depend sensitively on the degree of atomic order on the different crystallographic sites. In this work we demonstrate the magnetic contrast between bulk and thin-film samples of the Heusler alloy V$_{2}$FeAl. Arc-melted bulk ingots show practically no site preference of the elements (A2 structure), whereas magnetron-sputtered thin-film samples display a higher degree of atomic ordering with a tendency towards XA-type order. Electronic structure calculations favour ferrimagnetic XA-type ordering, and the effect of different pairwise atomic disorder on the element specific and net magnetic moments are evaluated to reproduce experimental observations. XA-type thin-films with iron moment of 1.24 $\mu_{\mathrm{B}}$ determined by X-ray magnetic circular dichroism are in agreement with calculation, but the measured net moment of 1.0 $\mu_{\mathrm{B}}$ per formula unit and average vanadium moment are smaller than expected from calculations. The measured Curie temperature is approximately 500 K. Films with a higher degree of disorder have a T$_{\mathrm{C}}$ close to 300 K with a net moment of 0.1 $\mu_{\mathrm{B}}$ at low temperature. The large calculated vanadium moments are destroyed by partial disorder on $4d$ vanadium sites. By contrast, the arc-melted and annealed bulk alloy with a fully-disordered A2 structure shows no spontaneous magnetization; it is a Pauli paramagnet with dimensionless susceptibility $\chi_{\mathrm{v}}=-2.95\times10^{-4}$.