scholarly journals Skyrmions and Spin Waves in Magneto–Ferroelectric Superlattices

Entropy ◽  
2020 ◽  
Vol 22 (8) ◽  
pp. 862
Author(s):  
Ildus F. Sharafullin ◽  
Hung T. Diep
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Triangular Lattice ◽  
Applied Field ◽  
Zero Field ◽  
Ferroelectric Films ◽  
Dm Interaction ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice

We present in this paper the effects of Dzyaloshinskii–Moriya (DM) magneto–electric coupling between ferroelectric and magnetic interface atomic layers in a superlattice formed by alternate magnetic and ferroelectric films. We consider two cases: magnetic and ferroelectric films have the simple cubic lattice and the triangular lattice. In the two cases, magnetic films have Heisenberg spins interacting with each other via an exchange J and a DM interaction with the ferroelectric interface. The electrical polarizations of ±1 are assumed for the ferroelectric films. We determine the ground-state (GS) spin configuration in the magnetic film and study the phase transition in each case. In the simple cubic lattice case, in zero field, the GS is periodically non collinear (helical structure) and in an applied field H perpendicular to the layers, it shows the existence of skyrmions at the interface. Using the Green’s function method we study the spin waves (SW) excited in a monolayer and also in a bilayer sandwiched between ferroelectric films, in zero field. We show that the DM interaction strongly affects the long-wave length SW mode. We calculate also the magnetization at low temperatures. We use next Monte Carlo simulations to calculate various physical quantities at finite temperatures such as the critical temperature, the layer magnetization and the layer polarization, as functions of the magneto–electric DM coupling and the applied magnetic field. Phase transition to the disordered phase is studied. In the case of the triangular lattice, we show the formation of skyrmions even in zero field and a skyrmion crystal in an applied field when the interface coupling between the ferroelectric film and the ferromagnetic film is rather strong. The skyrmion crystal is stable in a large region of the external magnetic field. The phase transition is studied.

scholarly journals Spin Waves and Skyrmions in Magneto-Ferroelectric Superlattices: Theory and Simulation†

Proceedings ◽  
2019 ◽  
Vol 46 (1) ◽  
pp. 3
Author(s):  
Hung Diep ◽  
Ildus Sharafullin
Keyword(s):  
Spin Waves ◽  
Wave Length ◽  
Magnetic Films ◽  
Zero Field ◽  
Ferroelectric Films ◽  
Spin Configuration ◽  
Dm Interaction ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice

We present in this paper the effects of Dzyaloshinskii–Moriya (DM) magnetoelectric coupling between ferroelectric and magnetic layers in a superlattice formed by alternate magnetic and ferroelectric films. Magnetic films are films of simple cubic lattice with Heisenberg spins interacting with each other via an exchange J and a DM interaction with the ferroelectric interface. Electrical polarizations of ± 1 are assigned at simple cubic lattice sites in the ferroelectric films. We determine the ground-state (GS) spin configuration in the magnetic film. In zero field, the GS is periodically non-collinear (helical structure) and in an applied field H perpendicular to the layers, it shows the existence of skyrmions at the interface. Using the Green’s function method we study the spin waves (SW) excited in a monolayer and also in a bilayer sandwiched between ferroelectric films, in zero field. We show that the DM interaction strongly affects the long-wave length SW mode. We calculate also the magnetization at low temperatures. We use next Monte Carlo simulations to calculate various physical quantities at finite temperatures such as the critical temperature, the layer magnetization and the layer polarization, as functions of the magneto-electric DM coupling and the applied magnetic field. Phase transition to the disordered phase is studied.

scholarly journals Effect of Anisotropy on the Critical Behaviour of Three- Dimensional Heisenberg Ferromagnets

1976 ◽  
Vol 31 (1) ◽  
pp. 34-40 ◽  
Author(s):  
R. Shanker ◽  
R. A. Singh
Keyword(s):  
Three Dimensional ◽  
Experimental Investigations ◽  
Isotropic Case ◽  
Zero Field ◽  
Critical Temperatures ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice ◽  
Anisotropic System ◽  
Critical Temperature Tc

The anisotropic nearest-neighbour Heisenberg model for the simple cubic lattice has been investigated by interpolating the anisotropy between the Ising and isotropic Heisenberg limits via general spin high-temperature series expansions of the zero-field suspectibility. This is done by estimating the critical temperature (Tc(3)) and the susceptibility exponent γ from the analysis of the series by the Ratio and Pade approximants methods. It is noted that Tc(3) varies with anisotropy while γ is almost the same for the anisotropic system, and a jump in it occurs for the isotropic case in agreement with the universality hypothesis. The effect of anisotropy on the susceptibility is also shown. Further, it is seen that estimates of γ for the two extreme limits agree well with those of previous theoretical as well as experimental investigations. In addition, critical temperatures have been summarised in a relation, and expressions for the magnetisation have been derived.

scholarly journals PHASE TRANSITION IN THE HEISENBERG FULLY-FRUSTRATED SIMPLE CUBIC LATTICE

2011 ◽  
Vol 25 (12n13) ◽  
pp. 929-936 ◽  
Author(s):  
V. THANH NGO ◽  
D. TIEN HOANG ◽  
H. T. DIEP
Keyword(s):  
Phase Transition ◽  
Statistical Physics ◽  
Spin Model ◽  
Order Transition ◽  
Heisenberg Spin ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice ◽  
Second Order Transition ◽  
Frustrated Spin

The phase transition in frustrated spin systems is a fascinating subject in statistical physics. We show the result obtained by the Wang–Landau flat histogram Monte Carlo simulation on the phase transition in the fully frustrated simple cubic lattice with the Heisenberg spin model. The degeneracy of the ground state of this system is infinite with two continuous parameters. We find a clear first-order transition in contradiction with previous studies which have shown a second-order transition with unusual critical properties. The robustness of our calculations allows us to conclude this issue putting an end to the 20-year long uncertainty.

Upper Bounds for the Connective Constant of Self-Avoiding Walks

1993 ◽  
Vol 2 (2) ◽  
pp. 115-136 ◽  
Author(s):  
Sven Erick Alm
Keyword(s):  
Large Class ◽  
Triangular Lattice ◽  
Upper Bounds ◽  
Square Lattice ◽  
Numerical Application ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice ◽  
Connective Constant ◽  
Self Avoiding Walks

We present a method for obtaining upper bounds for the connective constant of self-avoiding walks. The method works for a large class of lattices, including all that have been studied in connection with self-avoiding walks. The bound is obtained as the largest eigenvalue of a certain matrix. Numerical application of the method has given improved bounds for all lattices studied, e.g. μ < 2.696 for the square lattice, μ < 4.278 for the triangular lattice and μ < 4.756 for the simple cubic lattice.

Lower bound approximation to the free energy of an Ising model on a simple cubic lattice

1981 ◽  
Vol 59 (10) ◽  
pp. 1291-1295 ◽  
Author(s):  
Chin-Kun Hu ◽  
Wen-Den Chen ◽  
Yu-Ming Shih ◽  
Dong-Chung Jou ◽  
C. K. Pan ◽  
...  
Keyword(s):  
Free Energy ◽  
Ising Model ◽  
Lower Bound ◽  
Variational Method ◽  
Critical Point ◽  
Zero Field ◽  
Free Energies ◽  
Cubic Lattice ◽  
Simple Cubic ◽  
Simple Cubic Lattice

We apply a modified Kadanoff's variational method to calculate the lower bound zero-field free energies and their derivatives for an Ising model on the simple cubic lattice. We find a critical point at Kc = 0.2393769 with precision ±10−7.

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