The iridium double perovskite Sr2YIrO6 revisited: A combined structural and specific heat study

Abstract

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 non-magnetic 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. Here, we demonstrate the clue role of single crystal X-ray diffraction on the structural characterization of the Sr${}_2$YIrO${}_6$ double perovskite crystals by reporting the detection of a $\sqrt{2}a\times \sqrt{2}a\times 1c$ supercell, where $a$, $b$ and $c$ are the unit cell dimensions of the reported monoclinic subcell. In agreement with the expected non-magnetic 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 $n\sim 0.5(2)$ \%. These impurities lead to non-negligible spin correlations, which nonetheless, are not associated with long-range magnetic ordering.

20 pages, 10 figures