Off-stoichiometric effect on magnetic and electron transport properties of FeVAl in respect to NiVAl; Comparative study
arXiv:2401.12218 · doi:10.1103/PhysRevB.109.165105
Abstract
Density functional theory (DFT) calculations confirm that the structurally ordered FeVAl Heusler alloy is nonmagnetic narrow-gap semiconductor. This compound is apt to form various disordered modifications with high concentration of antisite defects. We study the effect of structural disorder on the electronic structure, magnetic, and electronic transport properties of the full Heusler alloy FeVAl and its off-stoichiometric equivalent FeVAl. Data analysis in relation to {\it ab initio} calculations indicates an appearance of antisite disorder mainly due to Fe--V and Fe--Al stoichiometric variations. The data for weakly magnetic FeVAl are discussed in respect to NiVAl. FeVAl can be classified as a nearly ferromagnetic metal with a pronounced spin glassy contribution, which, however, does not give a predominant effect on its thermoelectric properties. The figure of merit is at 300 K about 0.05 for the Fe sample and 0.02 for Ni one, respectively. However, it is documented that the narrow band resulting from Fe/V site exchange can be responsible for the unusual temperature dependencies of the physical properties of the Fe2TiAl alloy, characteristic of strongly correlated electron systems. As an example, the magnetic susceptibility of FeVAl exhibits singularity characteristic of a Griffiths phase, appearing as an inhomogeneous electronic state below K. We also performed numerical analysis which supports the Griffiths phase scenario.
19 pages, 22 figures