A dynamical phase transition in ferromagnetic granular materials

TL;DR

This paper investigates a temperature-driven dynamical phase transition in ferromagnetic granular materials, revealing a second order transition characterized by fractal clusters and power-law distributions through Monte Carlo simulations.

Contribution

The study introduces a detailed simulation of magnetic dynamics in disordered granular systems, identifying a second order phase transition with specific critical phenomena.

Findings

Identification of a transition from blocked to unblocked magnetic phases

Observation of fractal giant clusters at critical temperature

Power law distribution of cluster sizes near criticality

Abstract

We study, using simulations the dynamical properties of complex ferromagnetic granular materials. The system of grains is modeled by a disordered two-dimensional lattice in which the grains are embedded, while the magnitude and direction of the easy axis are random. Using the monte-carlo method we track the dynamics of the magnetic moments of the grains. We observe a transition of the system from a macroscopic blocked (ferromagnetic) phase at low temperature in which the grain's magnetic moment do not flip to the other direction to an unblocked (superparamagnetic) phase at high temperature in which the magnetic moment is free to rotate. Our results suggest that this transition exhibits the characteristics of a second order phase transition such as the appearance of a giant cluster of unblocked grains which is fractal at the critical temperature, a peak in the size of the second largest cluster at the same temperature and a power law distribution of cluster sizes near the criticality.