Disorder-mediated quenching of magnetization in NbVTiAl: Theory and Experiment

TL;DR

This study investigates the structural, electronic, and magnetic properties of NbVTiAl alloy, revealing how disorder affects its magnetic behavior and resolving discrepancies between theoretical predictions and experimental results.

Contribution

The paper provides a comprehensive analysis of disorder effects in NbVTiAl, explaining the discrepancy between predicted half-metallicity and observed ferrimagnetism.

Findings

NbVTiAl exhibits A2-type structure with disorder confirmed by XRD.

Experimental data shows near-zero magnetic moment, indicating compensated ferrimagnetism.

Disorder causes finite states at Fermi level, reducing spin polarization.

Abstract

In this paper, we present the structural, electronic, magnetic and transport properties of a equiatomic quaternary alloy NbVTiAl. The absence of (111) and (200) peaks in X-ray diffraction (XRD) data confirms the A2-type structure. Magnetization measurements indicate a high Curie temperature and a negligibly small magnetic moment ($\sim 10^{-3} \mu_B/f.u.$) These observations are indicative of fully compensated ferrimagnetism in the alloy. Temperature-dependent resistivity indicates metallic nature. Ab-initio calculation of fully ordered NbVTiAl structure confirms a nearly half metallic behavior with a high spin polarization ($\sim$ 90 \%) and a net magnetic moment of 0.8 $\mu_B/f.u.$ (in complete contrast to the experimental observation). One of the main objective of the present paper is to resolve and explain the long-standing discrepancy between theoretical prediction and experimental observation of magnetization for V-based quaternary Heusler alloys, in general. To gain an in-depth understanding, we modelled various disordered states and its subsequent effect on the magnetic and electronic properties. The discrepancy is attributed to the A2 disorder present in the system, as confirmed by our XRD data. The presence of disorder also causes the emergence of finite states at the Fermi level, which impacts the spin polarization of the system.