Metastability in graded and step like variation of field and anisotropy of the Blume-Capel ferromagnet

TL;DR

This study investigates metastable behavior in a 2D anisotropic Blume-Capel ferromagnet under graded and stepped magnetic fields and anisotropies, revealing how field and anisotropy gradients influence reversal dynamics and metastable lifetimes.

Contribution

The paper introduces a comprehensive Monte Carlo simulation analysis of metastability in graded and stepped anisotropic systems, highlighting the effects of spatial variations on reversal times and interface motion.

Findings

Reversal time scales with system size and field gradient as per a proposed scaling relation.

Interface motion follows hyperbolic tangent behavior under gradients.

A marginal competition line separates field-dominated and anisotropy-dominated reversal regimes.

Abstract

The metastable behaviour of two dimensional anisotropic Blume-Capel ferromagnet, under the influence of graded and stepped like variations of magnetic field, has been investigated by extensive Monte Carlo simulation using Metropolis single spin flip algorithm. Starting from the initial perfectly ordered state, reversal of magnetisation has been studied in presence of the field. Metastable lifetime or the reversal time of magnetisation for the system having uniform anisotropy and in the presence of both graded and stepped field has been studied. Also the same has been explored for a {\it graded and stepped anisotropic system} in presence of a uniform field. Finite size effect is analyzed for the variation of reversal time with gradient of field ($G_h$) and a scaling relation $\langle \tau \rangle \sim L^{-\beta} f(G_h L^\alpha)$ is proposed. Spatial variation of density profile for the projection states (i.e., +1, 0 and -1) has also been studied at the moment of reversal of magnetisation. The spatial variation of the number of spin flips per site is studied. Motion of the interface (or domain wall) with the gradient of field and gradient of anisotropy are investigated and are found to follow the hyperbolic tangent like behaviours in both cases. Since, both the anisotropy and the applied field have significant impact on the metastable lifetime, an interesting competitive scenario is observed for a {\it graded anisotropic system in graded field} and a {\it stepped anisotropic system in stepped field}. A line of marginal competition has been found out for both the cases separating the regions of field dominated reversal and anisotropy dominated reversal. The decay of the metastable volume fraction was found to follow the Avrami's law. The mean reversal time was observed to decrease monotonically across the phase boundary of the ferro-para transition.