We report the results of ${}^{151}\text{E}\text{u}$ Mössbauer effect and magnetization measurements in the Eu-doped ${\text{Ca}}_3{\text{Co}}_2{\text{O}}_6$ and ${\text{Ca}}_3{\text{CoRhO}}_6$, 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 Mössbauer spectra below a certain temperature $\left(T^{\ast }\right)$ 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 $T^{\ast }$ with the paramagnetic Curie temperature (a measure of intrachain coupling strength in these cases).

• Received 25 March 2008

DOI:https://doi.org/10.1103/PhysRevB.77.172403