arXiv subjects

Malcolm J. Grimson

Publications and source records attributed to Malcolm J. Grimson.

8 recordsLinked to original sources

arXiv2016

Dynamic Response in a Finite Size Composite Multiferroic Thin Film

Composite multiferroics, heterostructures of ferromagnetic (FM) and ferroelectric (FE) materials, are characterized by a remarkable magnetoelectric effect at the interface. Previous work has supported the ferromagnetic structure with magnetic spins and the ferroelectric with pseudospins which act as electric dipoles in a microscopic model, coupled with a magnetoelectric interaction [J. Appl. Phys. 118, 124109 (2015)]. In this work, by solving the stochastic Landau-Lifshitz-Gilbert equation, the electric-field-induced magnetization switching in a twisted boundary condition has been studied, and a behavior of domain wall in the ferromagnetic structure is discussed.

cond-mat.mes-hall↗

arXiv2016

Driving Skyrmions on a Composite Multiferroic Lattice

Magnetic skyrmions and multiferroics are the most interesting objects in nanostructure science that have great potential in future spin-electronic technology. The study of the multiferroic skyrmions has attracted much interest in recent years. This paper reports on the magnetic skyrmions induced by an electric driving field on a composite multiferroic lattice. By using the spin dynamics method, we use a classical magnetic spin model and an electric pseudospin model, which are coupled by a strong magnetoelectric coupling in the dynamical simulations. Interestingly, we observe some skyrmion-like objects on the electric component during the switching process, which is due to the connection between the electric and the magnetic structures.

cond-mat.mes-hall↗

arXiv2015

Pseudo-Spin Based Dynamical Model for Polarisation Switching in Ferroelectrics

A microscopic view of the response of the electric dipoles to a dynamic external field in a ferroelectric (FE) chain has been studied by two spin dynamics methods. One is the prominent micromagnetic approach, and the other is the micromagnetic approach with a variable size of the pseudo-spin. The energy stored in the ferroelectric chain is described by the transverse Ising model (TIM) with electric pseudo-spins. The simulations are based on a modified Landau-Lifshitz-Gilbert (LLG) equation which is precession free. The results obtained are shown and compared with the result supplemented by Landau-Devonshire (L-D) theory in the Appendix.

cond-mat.mes-hall↗

arXiv2015

Spin Dynamics in Driven Composite Multiferroics

A spin dynamics approach has been used to study the behavior of the magnetic spins and the electric pseudo-spins in a 1-D composite multiferroic chain with a linear magneto-electric coupling at the interface. The response is investigated with either external magnetic or electric fields driving the system. The spin dynamics is based on the Landau-Lifshitz-Gilbert equation. A Gaussian white noise is later added into the dynamic process to include the thermal effects. The interface requires a closer inspection of the magneto-electric effects. Thus, we construct a 2-D ladder model to describe the behavior of the magnetic spins and the electric pseudo-spins with different magneto-electric couplings.

cond-mat.mes-hall↗

arXiv2015

Spin Dynamics Simulation of the Magneto-Electric Effect in a Composite Multiferroic Chain

A composite multiferroic chain with an interfacial linear magneto-electric coupling is used to study the magnetic and electric responses to an external magnetic or electric field. The simulation uses continuous spin dynamics through the Landau-Lifshitz-Gilbert equations of the magnetic spin and the electric pseudo-spin. The results demonstrate an accurate description of the distribution of the magnetisation and polarisation are induced by applied electric and magnetic field, respectively.

cond-mat.mes-hall↗

arXiv2004

Stochastic dynamics and the dynamic phase transition in thin ferromagnetic films

The dynamic phase behavior of a classical Heisenberg spin system with a bilinear exchange anisotropy in a planar thin film geometry has been investigated by Monte Carlo simulations using different forms for the stochastic dynamics. In simulations of the dynamic phase transition (DPT) in films subject to a pulsed oscillatory external field with competing surface fields, both Glauber and Metropolis dynamics show a continuous DPT. Furthermore the field amplitude dependence of the DPT is qualitatively similar for both Glauber and Metropolis dynamics. However, the temperature dependence of the DPT is markedly different with the DPT being much sharper for Glauber dynamics. The difference arises from a decoupling of the surface and bulk responses of the film near the dynamic phase transition with Metropolis dynamics that is not evident for Glauber dynamics.

cond-mat.stat-mech↗

arXiv2003

Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films

Monte Carlo simulations have been performed to investigate the dependence of the dynamic phase behavior on the bilinear exchange anisotropy of a classical Heisenberg spin system. The system under consideration is a planar thin ferromagnetic film with competing surface fields subject to a pulsed oscillatory external field. The results show that the films exhibit a single discontinuous dynamic phase transition (DPT) as a function of the anisotropy of the bilinear exchange interaction in the Hamiltonian. Furthermore there is no evidence of stochastic resonance (SR) associated with the DPT. These results are in marked contrast to the continuous DPT observed in the same system as a function of temperature and applied field strength for a fixed bilinear exchange anisotropy.

cond-mat.stat-mech↗

arXiv2003

Dynamic phase transitions in thin ferromagnetic films

Monte Carlo simulations have been used to investigate the dynamic phase behavior of a classical Heisenberg spin system with a bilinear exchange anisotropy in a planar thin film geometry. Studies of the field amplitude, frequency and temperature dependence show dynamic phase transitions in films subject to a pulsed oscillatory external field. Thin films with competing surface fields show separate and distinct dynamic phase transitions for the bulk and surface layers of the film. Between the two transitions, a mixed state with coexisting dynamically ordered and dynamically disordered phases is observed in the film. In contrast, the free film with no surface fields shows a single dynamic phase transition as in a bulk system.

cond-mat.stat-mech↗