Magnetization plateau of the S=2 antiferromagnetic Heisenberg chain with anisotropies*

The magnetization process of the S=2 antiferromagnetic quantum spin chain with the exchange and single-ion anisotropies is investigated, using thenumerical exact diagonalization of finite-size clusters and the level spectroscopy analysis[1]. It is found that a magnetization plateau possibly appears at a half of the saturation magnetization for some suitable anisotropy parameters. The level spectroscopy analysis indicates that the 1/2 magnetization plateau is formed by two different mechanisms, depending on the anisotropy parameters. The phase diagram of the 1/2 plateau states and some typical magnetization curves are also presented. In addition the biquadratic interaction is revealed to enhance the plateau induced by the Haldane mechanism.
[1] T. Sakai, K. Okamoto and T. Tonegawa, Phys. Rev. B 100 (2019) 054407.