Transport and thermal properties of weakly ferromagneticSr2IrO4

Abstract

We have synthesized polycrystallineSr2IrO4 and measured its magnetic susceptibility, electrical resistivity, specific heat,Seebeck coefficient, and thermal conductivity. The magnetic susceptibilityχ(T) shows a ferromagnetic transition at 250 K while the behaviour above the transitiontemperature is well described by a Curie–Weiss fit with a small effective momentμeff = 0.33 μB and a paramagnetic Curie–Weiss temperature,θCW = +251 K, consistent with previous studies on this compound. However, specific heat, Seebeckcoefficient, and thermal conductivity are all dominated by the phonon contribution andshow no anomalies at the ferromagnetic transition. Electrical resistivity, unlike the singlecrystal, shows a huge increase, three orders of magnitude, with decreasing temperature.The temperature dependence of resistivity is logarithmic at high temperatures(210 K<T<350 K), Arrhenius type in intermediate temperatures(110 K<T<190 K) with a smallenergy gap of Δ = 37 meV, and variable-range-hopping type at low temperatures(35 K<T<80 K), in contrast to the data reported for single crystals. These results can be understood iflocalized states are present near the Fermi level due to structural oxygen disorder in thislow dimensional compound.