Nonequilibrium phase transition in spin-S Ising ferromagnet driven by Propagating and Standing magnetic field wave

TL;DR

This study investigates nonequilibrium phase transitions in spin-S Ising ferromagnets driven by propagating and standing magnetic field waves, revealing how the transition temperature and phase boundaries depend on spin value and field amplitude.

Contribution

It provides a detailed Monte Carlo simulation analysis of dynamical phase transitions in spin-S Ising models under different magnetic wave excitations, highlighting the effects of spin magnitude and field strength.

Findings

Phase transition from propagating to pinned phase with cooling.

Transition temperature decreases as spin S increases.

Phase boundary shrinks with higher spin S.

Abstract

The dynamical response of spin-S (S=1, 3/2, 2, 3) Ising ferromagnet to the plane propagating wave , standing magnetic field wave and uniformly oscillating field with constant frequency are studied separately in two dimensions by extensive Monte Carlo simulation. Depending upon the strength of the magnetic field and the value of the spin state of the Ising spin lattice two different dynamical phases are observed. For a fixed value of S and the amplitude of the propagating magnetic field wave the system undergoes a dynamical phase transition from propagating phase to pinned phase as the temperature of the system is cooled down. Similarly in case with standing magnetic wave the system undergoes dynamical phase transition from high temperature phase where spins oscillates coherently in alternate bands of half wavelength of the standing magnetic wave to the low temperature pinned or spin frozen phase. For a fixed value of the amplitude of magnetic field oscillation the transition temperature is observed to decrease to a limiting value as the value of spin S is increased. The time averaged magnetisation over a full cycle of the magnetic field oscillation plays the role of the dynamic order parameter. A comprehensive phase boundary is drawn in the plane of magnetic field amplitude and dynamic transition temperature. It is found that the phase boundary shrinks inwards for high value of spin state S. Also in the low temperature (and high field) region the phase boundaries are closely spaced.