Ferromagnetically correlated clusters in semimetallic Ru2NbAl Heusler alloy and its thermoelectric properties

Abstract

In this work, we report the structural, magnetic, 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 γ (∼2.7mJmol-1K-2) as well as the linear nature of temperature dependence of the Seebeck coefficient indicate a semimetallic ground state with a pseudogap, which 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 nondoped full Heusler alloys.