Structural and magnetic anomalies among the spin-chain compounds, Ca3Co1+xIr1–xO6

The results of X-ray diffraction, and ac and dc magnetisation as a function of temperature are reported for a new class of spin-chain oxides, Ca3Co1+x Ir1–xO6. While the x =0,0.0,3.0,5 and 10 are found to form in the K4CdCl6-derived rhombhohedral (space group R3c) structure, the x = 07 composition is found to undergo a monoclinic distortion in contrast to a literature report. Apparently, the change in the crystal symmetry with x manifests itself as a change in the sign of paramagnetic Curie temperature for this composition as though magnetic coupling sensitively depends on such crystallographic distortions. All the compositions exhibit spin-glass anomalies with an unusually large frequency dependence of the peak temperature in ac susceptibility in a temperature range below 50 K, interestingly obeying Vogel–Fulcher relationship even for the stoichiometric compounds.