Critical Responses to Magnetic Field for Fully-Frustrated Square Ising Spin Systems

Abstract

We simulate many kinds of fully-frustrated square Ising systems under the uniform magnetic field and observe various types of dependence of the magnetization on the field at low temperatures. For some systems, a critical dependence is observed; the response exhibits the scaling law belonging to the Villain-Stephenson universality class of δ=7. For other systems, a non-critical dependence (δ=1) and a marginal one are observed. Based on an idea of the partially disordered state, we propose a simplified method which can predict whether the response to the uniform field is critical or not. We examine possible changes in critical exponents through a mechanism of cancellation among the spin pair correlation functions.