Structural and magnetic properties of spin chain compounds Ca₃Co_2-xFe_xO₆

Abstract

We report the structural and magnetic properties of quasi-one-dimensional (1D) spin chain compounds Ca₃Co_2-xFe_xO₆ (x=0, 0.1, 0.2, and 0.4). Simultaneous Rietveld refinement of powder neutron and x-ray diffraction patterns at room temperature confirmed the single-phase formation for all the samples in the rhombohedral structure with space group R3c. Rietveld refinement and Mössbauer study confirmed that Fe³⁺ ion was doped at trigonal prism site, 6a (0, 0, 1∕4) of Co. Decrease of intrachain positive exchange constant J and increase of interchain negative exchange constant J′ with iron substitution result in deviation from "1D character" in these spin chain compounds. Deviation from the H^−3∕2 dependence of magnetization-approach to its saturation value for higher iron concentration (x = 0.4) further supports this observation. The observed results have been ascribed to a breaking of the ferromagnetically ordered linear spin chains along the crystallographic c axis with iron doping and strengthening of antiferromagnetic exchange interaction between Fe³⁺ ions.