Thermal conductivity, electron transport, and magnetic properties of single-crystal Ca3Co2O6

A recent neutron-diffraction study on the magnetic insulator Ca3Co2O6 shows that spins in the c-axis chains of alternating Co1 octahedral and Co2 trigonal-prismatic face-sharing CoO6/2 sites are ordered below T-N with a long-wavelength modulation instead of a simple ferromagnetic chain as thought previously. Frustrated antiferromagnetic interchain interactions compete with ferromagnetic intrachain coupling to invalidate an Ising model despite a strong spin-orbit coupling lambda L center dot S on the Co2 ions. We have carried out thermal conductivity, electron transport, and magnetic measurements on single-crystal Ca3Co2O6 in order to characterize this complicated magnetic system. An anisotropic thermal-conductivity component superimposed at high temperatures on an isotropic phonon component is consistent with an exchange-interaction-mediated heat transfer. This observation is incompatible with an Ising model. The ferromagnetic intrachain interactions are argued to reflect a one-dimensional itinerant-electron band that is split by the c-axis translational symmetry and the on-site intra-atomic Hund exchange interaction with a localized S=3/2 spin on the Co2 ions.