Nonmonotonical crossover of the effective susceptibility exponent

TL;DR

This study numerically investigates how the magnetic susceptibility exponent in 2D spin systems transitions from classical to Ising-like behavior, revealing a nonmonotonic crossover in the ordered phase and supporting universality of the crossover function.

Contribution

It provides the first detailed numerical analysis of the nonmonotonic crossover of the susceptibility exponent in 2D spin systems with varying interaction ranges.

Findings

The effective susceptibility exponent gamma_eff exhibits a nonmonotonic change in the ordered phase.

The crossover from classical to Ising behavior spans several decades in reduced temperature.

The universality of the crossover function is supported by the results.

Abstract

We have numerically determined the behavior of the magnetic susceptibility upon approach of the critical point in two-dimensional spin systems with an interaction range that was varied over nearly two orders of magnitude. The full crossover from classical to Ising-like critical behavior, spanning several decades in the reduced temperature, could be observed. Our results convincingly show that the effective susceptibility exponent gamma_eff changes nonmonotonically from its classical to its Ising value when approaching the critical point in the ordered phase. In the disordered phase the behavior is monotonic. Furthermore the hypothesis that the crossover function is universal is supported.