Anisotropic magnetic properties of Ca3Co4O9:: Evidence for a spin-density-wave transition at 27 K -: art. no. 104410

The dc susceptibility chi of single crystal platelets of Ca3Co4O9 was measured in applied magnetic fields H below 55 kOe. At temperatures below 400 K, the crystals exhibited three magnetic transitions successively at T(SS)similar to380 K, T-SDW=27 K, and T-ferri=19 K. The highest spin state (SS) transition was found to be discontinuous with the appearance of a thermal hysteresis loop about 20 K wide. At 27 K, a small shoulder in the chi(T) curve was observed only for Hperpendicular toab, indicating the formation of an incommensurate spin-density-wave (SDW) state, which was also confirmed by independent muon spin rotation and relaxation experiments. The lowest of T-ferri is a transition to a ferrimagnetic state, for which also a ferrimagnetic hysteresis loop was observed for Hperpendicular toab, but not for Hparallel toab. This anisotropic behavior indicated that the ferrimagnetic interaction is parallel to the c axis. Considering the alternating stacking structure of Ca3Co4O9 along the c axis, the ferrimagnetism is most likely caused by interlayer coupling between the [Ca2CoO3] and [CoO2] subsystems.