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 electron spin resonance (ESR) spectroscopy results on the double perovskite Ba_{2}YIrO_{6}. On general grounds, this material is expected to be nonmagnetic due to the strong coupling of the spin and orbital momenta of Ir^{5+} (5d^{4}) ions. However, controversial experimental reports on either strong antiferromagnetism with static order at low temperatures or just a weakly paramagnetic behavior have triggered a discussion on the breakdown of the generally accepted scenario of the strongly spin-orbit coupled ground states in the 5d^{4} iridates and the emergence of a novel exotic magnetic state. Our data evidence that the magnetism of the studied material is solely due to a few percent of Ir^{4+} and Ir^{6+} magnetic defects while the regular Ir^{5+} sites remain nonmagnetic. Remarkably, the defect Ir^{6+} species manifest magnetic correlations in the ESR spectra at T≲20  K, suggesting a long-range character of superexchange in the double perovskites as proposed by recent theories.

We present a combined experimental and theoretical study of the elementary magnetic excitations in Ba 2 YIrO 6 and Sr 2 YIrO 6-the two most intensively discussed candidates for a new type of magnetic instability caused by exciton condensation. For both materials, high-resolution resonant inelastic x-ray scattering (RIXS) at the Ir L 3 edge reveals sharp excitations around 370 and 650 meV energy loss, which we identify as triplet and quintet spin-orbit excitons. While the momentum-dependent RIXS spectra reveal that both the triplet and the quintet propagate coherently within the nonmagnetic background of the singlet sites, these modes remain fully gapped. The Ir-Ir exchange interactions in both double perovskites are therefore not strong enough to overcome the magnetic gap and, hence, our results exclude an intrinsic magnetic instability due to a condensation of magnetic excitations for both Ba 2 YIrO 6 and Sr 2 YIrO 6 .

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