Magnetic anomalies in the spin-chain system Sr₃Cu_1−xZn_xIrO₆

Abstract

We report the results of ac and dc magnetization (M) and heat-capacity (C) measurements on the solid solution, Sr₃Cu_1−xZn_xIrO₆. While the Zn end member is known to form in a rhombohedral pseudo one-dimensional K₄CdCl₆ structure with an antiferromagnetic ordering temperature of (T_N=) 19 K, the Cu end member has been reported to form in a monoclinically distorted form with a Curie temperature of (T_C=) 19 K. The magnetism of the Zn compound is found to be robust to synthetic conditions and is broadly consistent with the behavior known in the literature. However, we find a lower magnetic ordering temperature (T_o) for our Cu compound (~13 K), thereby suggesting that T_o is sensitive to synthetic conditions. The Cu sample appears to be in a spinglass- like state at low temperatures, judged by a frequency dependence of ac magnetic susceptibility and a broadening of the C anomaly at the onset of magnetic ordering, in sharp contrast to earlier proposals. Small applications of magnetic field, however, drive this system to ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x=0.75 or 0.25) significantly depress magnetic ordering; in other words, To varies non-monotonically with x (T_o~6, 3 and 4 K for x=0.25, 0.5, and 0.67 respectively). The plot of inverse susceptibility versus temperature is non-linear in the paramagnetic state as if correlations within (or among) the magnetic chains continuously vary with temperature. The results establish that this class of oxides is quite rich in physics.