Steplike Magnetization in a Spin-Chain System: ${\mathrm{Ca}}_3{\mathrm{Co}}_2{\mathrm{O}}_6$

Because of a ferromagnetic in-chain coupling between ${\mathrm{Co}}^{3+}$ ions at trigonal sites, ${\mathrm{Co}}_2{\mathrm{O}}_6$ chains are considered as large rigid spin moments. The antiferromagnetic Ising model on the triangular lattice is applied to describe an interchain ordering. An evolution of metastable states in a sweeping magnetic field is investigated by the single-flip technique. At the first approximation two steps in the magnetization curve and a plateau at $1/3$ of the saturation magnetization are found. Four steps in magnetization are determined in high-order approximations in agreement with experimental results.

Figure 1

The honeycomb magnetic structure. The black and white circles are spin-up and spin-down states, respectively; the gray circles can be either spin-up or spin-down states.

Figure 2

The magnetic moment as a function of the dimensionless magnetic field $B/J$. The dash, dash-dot, and solid lines are the results of the first, second, and fourth approximations, correspondingly. The four nearest-neighbor configurations producing the critical spin-flip fields are shown. Note the break in the vertical axis.

Figure 3

An arrangement containing the tripod configuration. The tripod is shown in the solid line. The three white circles close to the center of the tripod have 4 spin-up (the black circles) and 2 spin-down (the white circles) nearest neighbors.

Figure 4

Three tripods connected in the star arrangement. Three white circles close to the center of the star are surrounded by 5 spin-up and 1 spin-down nearest neighbors.