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

Abstract

In this work, we report the structural, magnetic and electrical and thermal transport properties of the Heusler-type alloy Ru 2 NbAl. 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 (∼2.7 mJ/mol-K 2 ), 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 Ru 2 NbAl, it is the largest among all the reported nondoped full Heusler alloys.

Half metallicity in Cr substituted Fe2TiSn

“…This upturn diminishes systematically with increasing Cr concentration in the series. As also demonstrated in Fe 2 VAl 17 and NbAl 18 Heuslers, such an upturn is mainly associated with the presence of magnetic clusters. Generally, the magnetic clusters present in any system rest at lowest energy at low temperature.…”

“…The additional terms, 2 , accommodates the magnetic cluster formation with the quantity N being the number of clusters present in the system. The term includes the extended temperature range beyond /50 as , the Debye temperature, has not been separately determined for these compositions 18 . The experimental data fit nicely to this equation in the temperature range (2–25) K, as shown in Fig.…”

Magnetic Full-Heusler Compounds for Thermoelectric Applications

“…Figure 10(b) shows the temperature dependence of zT for Co 2 MnSi calculated using the PF value (Figure 5(b)) and the κ tot value (Figure10(a)). Due to the high κ tot , the maximum zT value, zT max ,ofCo 2 MnSi is 0.039, which is obtained at temperatures above 900 K. Although this zT max value is far below the standard level of zT = 1, it is higher than that of Co 2 TiSn (0.033 at 370-400 K)[38] and those of semi-metallic full-Heusler compounds (0.0052 at 300 K for Ru 2 NbAl[28] and 0.0027 at 300 K for Ru 2 VAl 0.25 Ga 0.75[29]). It should be noted that the κ tot of Co 2 MnSi is not equal to the carrier thermal conductivity, κ e .…”

“…Since then, many studies have been dedicated to investigate the electronic and magnetic properties of ternary and quaternary full-Heusler compounds. It has been revealed that full-Heusler compounds exhibit a variety of electronic properties; they exhibit the properties of semiconductors [9][10][11][12][13][14][15][16][17][18], spingapless semiconductors (SGSs) [19][20][21][22][23][24][25][26], semimetals [27][28][29], metals [30][31][32][33][34] and half-metals (HMs) [32,. Considering the magnetic properties, they have been reported to exhibit nonmagnetism [9][10][11][14][15][16][17][18], ferromagnetism [12, 19-24, 30-33, 36-46, 48-58, 61-66, 68-78], ferrimagnetism [13,30,35,47,59,60,67] and antiferromagnetism [25,26,34].…”

First‐principles study on structural, electronic, magnetic, elastic, mechanical and thermodynamic properties of Mn 2 PtCo Heusler alloy

“…The HAs are remarkable due to their active role in the spin‐injection devices, 13‐17 spintronic devices and high thermoelectric performance, 18‐20 tunnelling magneto‐resistance, 21‐24 spin filters, 16 giant magneto resistance, 25,26 magnetic sensors, 27 non‐volatile magnetic random access memories, 28,29 electro‐mechanical applications 30 . The extensive theoretical 31‐35 and experimental 36‐40 studies of the HAs have been reported in the literature in context to the thermoelectric applications due to their high power factor and low thermal conductivities.…”