Dimensional crossover in the Ising antiferromagnet on the anisotropic triangular lattice at finite temperature

¹ Kyoto Sangyo University, Department of Physics, Faculty of Science - Kyoto 603-8555, Japan
² Aoyama-Gakuin University - 5-10-1, Fuchinobe, Sagamihara, Kanagawa 229-8558, Japan
³ Multiferroics Project (MF), ERATO, Japan Science and Technology Agency (JST), The University of Tokyo Tokyo 113-8656, Japan

^a chisa@cc.kyoto-su.ac.jp

Received: 14 May 2010
Accepted: 21 January 2011

Abstract

We study an Ising antiferromagnet on a triangular lattice which has interactions along three different directions via two J-bonds and one anisotropic J′-bond with J′ ≥ J. Although its finite-temperature state has long been considered as simply disordered, we find systematic generation of ferromagnetic J′-bonds named “good defects” each carrying the energy 2δ_J ≡ 2(J′−J). They exhibit eminent spacial correlation which is regarded as a soft lattice network. The specific heat shows a universal peak at T^* ∼ δ_J and the corresponding energy follows activation type of temperature dependence with an excitation gap 2δ_J. Energetics and crossover between this particular two-dimensional state and the other disordered or one-dimensional states are discussed.