Spin-chain magnetism in Eu-doped Ca₃Co₂O₆ and Ca₃CoRhO₆ investigated by Mossbauer spectroscopy

Abstract

We report the results of ¹⁵¹Eu Mossbauer effect and magnetization measurements in the Eu-doped Ca₃Co₂O₆ and Ca₃CoRhO₆, which are of great current interest in the fields of spin-chain magnetism and geometrical frustration. We find that there is a pronounced increase in the linewidth of the Mossbauer spectra below a certain temperature (T^∗) that is well above the one at which three-dimensional magnetic ordering features set in. This unusual broadening of the spectra indicates the existence of a characteristic temperature in these "exotic" magnetic systems, which is attributable to the onset of incipient one-dimensional magnetic order. This is inferred from an intriguing correlation of T^∗ with the paramagnetic Curie temperature (a measure of intrachain coupling strength in these cases).