Electronic properties of Sn & B doped Fe2VAl Heusler alloys

In this work we report a comprehensive study of Fe2VAl1-xMx (M=Sn, B, x = 0, 0.03, 0.06 and 0.1) alloys. Initially, the electronic properties for the parent compound, Fe2VAl have been studied and the role of various anti-site disorders on the electronic properties is predicted. The ab-initio calculations on ordered L21 structure of Fe2VAl alloy have been carried out by introducing B2, DO3, A2' and  XY-XZ type disorders in order to understand the role of anti-site disorder on magnetic and transport properties. The temperature dependence of transport and magnetization have been measured for Fe2VAl1-xSnx (x = 0, 0.03, 0.06, 0.1, 0.2 and 1) alloys which show high temperature semiconductor to low temperature metallic like behaviour and non-magnetic to short range magnetic behaviour while substituting Sn at Al-site. A sharp decrease in the electrical resistivity (ρ), and substantial enhancement in thermoelectric power (S) can be explained on the basis of the electronic band structure of the corresponding material in which the Fermi level shifts slightly from the middle of pseudogap. Theoretical calculations are done on these materials at their near by compositions, based on the density functional theory (DFT) using Wien2k and BoltzTrap software packages. Along with this, studies on structural, magnetotransport and magnetic dynamics aspects of Boron diluted Fe2VAl (Fe2VAl1-xBx (x=0.03, 0.06, 0.1, 0.2 and 0.5)) alloys are also presented. This partial substitution results in enhancement of magnetic as well as magnetotransport properties, in contrast with the theoretical reports. Further, a resistivity maximum (TP) is observed in the vicinity of magnetic transition temperature (TC) accompanied by a large (29%) negative magnetoresistance (nMR). Both TP and TC are observed to  be sensitive to the applied magnetic field, indicating a strong coupling between the magnetic and transport behaviours in these alloys.