The iridium double perovskites with Ir⁵⁺ revised. A combined structural and specific heat study

Recently, the iridate double perovskite Sr₂YIrO₆ has attracted considerable attention due to the report of unexpected magnetism in this Ir⁵⁺ material, in which according to the Jeff model, a non-magnetic ground state is expected. We present a structural, magnetic and thermodynamic characterization of Sr₂YIrO₆ and Ba₂YIrO₆ single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. In agreement with the expected non-magnetic ground state of Ir⁵⁺ (5d⁴) in these iridates, no magnetic transition is observed down to 430 mK. Moreover, our results suggest that the low temperature anomaly observed in the specific heat is not related to the onset of long-range magnetic order. Instead, it is identified as a Schottky anomaly caused by paramagnetic impurities present in the sample, of the order of 0.5(2) %. These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.