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Recently, the iridate double perovskite Sr 2 YIrO 6 has attracted considerable attention due to the report of unexpected magnetism in this Ir 5+ (5d 4 ) material, in which according to the J eff model, a nonmagnetic ground state is expected. However, in recent works on polycrystalline samples of the series Ba 2−x Sr x YIrO 6 no indication of magnetic transitions have been found. We present a structural, magnetic, and thermodynamic characterization of Sr 2 YIrO 6 single crystals, with emphasis on the temperature and magnetic field dependence of the specific heat. As determined by x-ray diffraction, the Sr 2 YIrO 6 single crystals have a cubic structure, with space group F m3m. In agreement with the expected nonmagnetic ground state of Ir 5+ (5d 4 ) in Sr 2 YIrO 6 , 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 n ∼ 0.5(2)%. These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

We report the structural, magnetic and thermodynamic properties of the double perovskite compound La 2 CuIrO 6 from X-ray, neutron diffraction, neutron depolarization, dc magnetization, ac susceptibility, specific heat, muon-spin-relaxation (µSR), electron-spin-resonance (ESR) and nuclear magnetic resonance (NMR) measurements. Below ∼ 113 K, short-range spin-spin correlations occur within the Cu 2+ sublattice. With decreasing temperature, the Ir 4+ sublattice progressively involves in the correlation process. Below T = 74 K, the magnetic sublattices of Cu (spin s = 1 2 ) and Ir (pseudospin j = 1 2 ) in La 2 CuIrO 6 are strongly coupled and exhibit an antiferromagnetic phase transition into a non-collinear magnetic structure accompanied by a small uncompensated transverse moment. A weak anomaly in ac-susceptibility as well as in the NMR and µSR spin lattice relaxation rates at 54 K is interpreted as a cooperative ordering of the transverse moments which is influenced by the strong spin-orbit coupled 5d ion Ir 4+ . We argue that the rich magnetic behavior observed in La 2 CuIrO 6 is related to complex magnetic interactions between the strongly correlated spin-only 3d ions with the strongly spin-orbit coupled 5d transition ions where a combination of the spin-orbit coupling and the low-symmetry of the crystal lattice plays a special role for the spin structure in the magnetically ordered state.

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