Magnetic Orderings and Néel Temperature of TbNi2B2C

We employ a two-ion model to calculate the spontaneous magnetization and susceptibility of TbNi2B2C with the mean-field theory, and derive an analytic formula for the Neel temperature of the material with the perturbation theory. In both the cases, only the four lowest crystal-electric-field (CEF) states are taken into account as base functions. Our theoretical results are consistent with the experimental data, manifesting the strong effects of the low lying CEF states on the magnetic behaviors of the material and the suitability of the theoretical approach proposed here.