Ferromagnetically correlated clusters in semi-metallic Ru2NbAl Heusler alloy

TL;DR

This study investigates the structural, magnetic, and transport properties of Ru2NbAl Heusler alloy, revealing semi-metallic behavior, ferromagnetic clusters, and the potential for thermoelectric applications despite low efficiency.

Contribution

It provides a comprehensive analysis of Ru2NbAl's magnetic and electronic properties, highlighting ferromagnetic clusters and semi-metallic ground state with potential thermoelectric relevance.

Findings

Presence of superparamagnetic clusters with Pauli paramagnetism

Development of short-range ferromagnetic interactions below 5 K

Largest ZT among non-doped full Heusler alloys

Abstract

In this work, we report the structural, magnetic and electrical and thermal transport properties of the Heusler-type alloy Ru2NbAl. From the detailed analysis of magnetization data, we infer the presence of superparamagnetically interacting clusters with a Pauli paramagnetic background, while short-range ferromagnetic interaction is developed among the clusters below 5 K. The presence of this ferromagnetic interaction is confirmed through heat capacity measurements. The relatively small value of electronic contribution to specific heat, gamma (~2.7 mJ/mol-K2), as well as the linear nature of temperature dependence of Seebeck coefficient indicate a semi-metallic ground state with a pseudo-gap that is also supported by our electronic structure calculations. The activated nature of resistivity is reflected in the observed negative temperature coefficient and has its origin in the charge carrier localization due to antisite defects, inferred from magnetic measurements as well as structural analysis. Although the absolute value of thermoelectric figure of merit is rather low (ZT = 5.2*10-3) in Ru2NbAl, it is the largest among all the reported non-doped full Heusler alloys.