Magnetization plateau and incommensurate spin modulation in Ca3Co2O6

The magnetic properties of a trigonal prism unit of the spin-2 frustrated compound Ca3Co2O6 are studied by means of the density-matrix renormalization group method. A magnetization plateau at $ms/3$ ($ms$ is the saturation magnetization) with ferrimagnetic structure is observed. By fitting the experimental data of magnetic curve, an estimation of the couplings gives J1=-26.84K, J_{2}=0.39K, and J_{3}=0.52K. The local magnetic moments are unveiled to exhibit an incommensurate sinusoidally modulation along the three chains of the trigonal prism, which gives a strong theoretical support to the experimentally observed incommensurate partially disordered antiferromagnetic state for Ca3Co2O6. The present result suggests that the modulation indeed originates from the competition of antiferromagnetic and ferromagnetic couplings.