The investigation of the critical phenomena of the competing spin systems with the higher order spin interaction on the bulk and thin film

点击翻译按钮获取中文摘要

The ANNNI and A3NNI models are familiar as the spin systems with the competition between interactions with different range (for example, 1st, 2nd, and 3rd nearest-neighbors). In this study, we consider the S=1 ANNNI and A3NNI models with the higher order spin interaction. Using the analytical methods and the Monte Carlo simulation (MC), we investigate the role and importance of the higher order spin interaction and the spin quantum number in the competing spin systems, theoretically.1) The extended A3NNI modelWe propose the extended A3NNI model with the higher order spin interaction as model explaining the phase transition from the k=1/3 modulated structure to the antiferromagnetic structure in UNi2Si2. The temperature dependence of the Fourier coefficients in the Modulated structures are calculated by MC, and we show the appearance of this phase transition.2) The extended ANNNI model on the thin filmUsing MC, the magnetic phase diagram of S=1 ANNNI model with the 3-site 4-spin interaction is obtained, and the finite-size scaling shows that 4 phase transition lines are the second order phase transition. These results suggest the existence of the tetracritical point.3) The extended ANNNI model with alternating intralayer interactionsUsing MC with non-equilibrium relaxation method and the finite-size scaling, we calculated critical temperatures and critical exponents. The obtained exponents show that the ordinary universality does not hold in this model, and suggests that the weak universality holds.