Journal of the Physical Society of Japan
Low Temperature Phase of a Dilute Axial-next-nearest-neighbor Ising Model in Two Dimensions
Fumitaka Matsubara, Nobuo Suzuki, Takayuki Shirakura
Abstract
We examine the ground state of a dilute two-dimensional axial-next-nearest-neighbor Ising model with the interaction ratio κ (≡ −J2/J1) > 1/2. We calculate the spin overlap function Q together with the antiphase (〈2〉 phase) magnetization M〈2〉 on medium lattices of L × L (L ≤ 24) using a cluster heat bath method. The 〈2〉 phase is destroyed by a small quantity of non-magnetic atoms due to a random impurity effect, and a critical phase is realized, which is composed of segments of four types of 〈2〉 domains arranged in order. As the spin concentration c decreases, a critical phase with different ferromagnetic clusters appears near above the percolation threshold cp of the lattice. A phase diagram is proposed in the \((\kappa ,c)\) plain at low temperatures.