scholarly journals AXIAL AND OFF-AXIAL DYNAMIC TRANSITIONS IN UNIAXIALLY ANISOTROPIC HEISENBERG FERROMAGNET: A COMPARISON

2003 ◽  
Vol 14 (01) ◽  
pp. 49-59 ◽  
Author(s):  
MUKTISH ACHARYYA
Keyword(s):  
Magnetic Field ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Order Parameter ◽  
Heisenberg Ferromagnet ◽  
Axial Field ◽  
Ising Ferromagnet ◽  
High Anisotropy ◽  
Different Temperatures ◽  
Dynamic Transitions

Uniaxially anisotropic Heisenberg ferromagnet, in the presence of a magnetic field varying sinusoidally in time, is studied by Monte Carlo simulation. The axial (field applied only along the direction of anisotropy) and off-axial (field applied only along the direction which is perpendicular to the direction of anisotropy) dynamic transitions are studied. By studying the distribution of the dynamic order parameter component, it is observed that the axial transition is discontinuous for low anisotropy and becomes continuous in high anisotropy. The off-axial transition is found to be continuous for all values of anisotropy. In the infinite anisotropy limit, both types of transitions are compared with that observed in an Ising ferromagnet for the same value of the field and frequency. The infinitely anisotropic axial transition and dynamic transition in the Ising ferromagnet occur at different temperatures, whereas the infinitely anisotropic off-axial transition and the equilibrium ferro-para transition in the Ising model occur at the same temperature.

OFF-AXIAL DYNAMIC SYMMETRY BREAKING IN UNIAXIALLY ANISOTROPIC HEISENBERG FERROMAGNET

2001 ◽  
Vol 12 (05) ◽  
pp. 709-716 ◽  
Author(s):  
MUKTISH ACHARYYA
Keyword(s):  
Magnetic Field ◽  
Monte Carlo ◽  
Transition Temperature ◽  
Monte Carlo Method ◽  
Symmetry Breaking ◽  
Specific Heat ◽  
Order Parameter ◽  
Three Dimensions ◽  
Heisenberg Ferromagnet ◽  
Dynamic Symmetry

The dynamics of uniaxially (along the z direction) anisotropic Heisenberg ferromagnets (in three dimensions) in the presence of a magnetic field varying sinusoidally in time (along the x-direction only) is studied by Monte Carlo method using Metropolis rate. The time averaged (over a complete cycle of the oscillating field) value of z component of the magnetization continuously vanishes at a particular transition temperature associated with a dynamic symmetry breaking of mz-hx loop. The temperature variation of dynamic order parameter and the dynamic specific heat for different values of the anisotropy show that the transition temperature increases as the strength of anisotropy increases.

scholarly journals NONEQUILIBRIUM PHASE TRANSITIONS IN MODEL FERROMAGNETS: A REVIEW

2005 ◽  
Vol 16 (11) ◽  
pp. 1631-1670 ◽  
Author(s):  
MUKTISH ACHARYYA
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Transition Point ◽  
Time Dependent ◽  
Heisenberg Ferromagnet ◽  
Dynamic Transition ◽  
Dynamic Phase ◽  
Nonequilibrium Dynamic ◽  
Dynamic Phase Transition ◽  
Dynamic Transitions

The thermodynamical behaviors of ferromagnetic systems in equilibrium are well studied. However, the ferromagnetic systems far from equilibrium became an interesting field of research in last few decades. Recent exploration of ferromagnetic systems in the presence of a steady magnetic field are also studied by using standard tools of equilibrium statistical physics. The ferromagnet in the presence of time-dependent magnetic field, shows various interesting phenomena. An usual response of a ferromagnet in the presence of a sinusoidally oscillating magnetic field is the hysteresis. Apart from this hysteretic response, the nonequilibrium dynamic phase transition is also a very interesting phenomenon. In this chapter, the nonequilibrium dynamic phase transitions of the model ferromagnetic systems in presence of time-dependent magnetic field are discussed. For this kind of nonequilibrium phase transition, one cannot employ the standard techniques of equilibrium statistical mechanics. The recent developments in this direction are mainly based on numerical simulation (Monte Carlo). The Monte Carlo simulation of kinetic Ising model, in presence of sinusoidally oscillating (in time but uniform over space) magnetic field, is extensively performed to study the nonequilibrium dynamic phase transition. The temperature variations of dynamic order parameter, dynamic specific heat, dynamic relaxation time etc. near the transition point are discussed. The appearance and behaviors of a dynamic length scale and a dynamic time scale near the transition point are also discussed. All these studies indicate that this proposed dynamic transition is a nonequilibrium thermodynamic phase transition. The disorder (quenched) induced zero temperature (athermal) dynamic transition is studied in random field Ising ferromagnet. The dynamic transition in the Heisenberg ferromagnet is also studied. The nature of this transition in the Heisenberg ferromagnet depends on the anisotropy and the polarisation of the applied time varying magnetic field. The anisotropic Heisenberg ferromagnet in the presence of elliptically polarised magnetic field shows multiple dynamic transitions. This multiple dynamic transitions in anisotropic Heisenberg ferromagnet are discussed here. Recent experimental evidences of dynamic transitions are also discussed very briefly.

scholarly journals MONTE CARLO SIMULATION OF ISING MODEL ON DIRECTED BARABASI–ALBERT NETWORK

2005 ◽  
Vol 16 (04) ◽  
pp. 585-589 ◽  
Author(s):  
MUNEER A. SUMOUR ◽  
M. M. SHABAT
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Ising Model ◽  
Monte Carlo Simulations ◽  
Characteristic Time ◽  
Spontaneous Magnetization ◽  
Zero Temperature ◽  
Different Temperatures ◽  
Large Systems ◽  
Ising Spins

The existence of spontaneous magnetization of Ising spins on directed Barabasi–Albert networks is investigated with seven neighbors, by using Monte Carlo simulations. In large systems, we see the magnetization for different temperatures T to decay after a characteristic time τ(T), which is extrapolated to diverge at zero temperature.

The Influnence of the Amplitude and Frequency of Sweeped Magnetic Field on the Exchange Bias and Coercivity for Ferromagnetic / Antiferromagnetic Films: Monte Carlo Simulation

2011 ◽  
Vol 694 ◽  
pp. 538-542
Author(s):  
Wen Ting Zheng ◽  
Li Qin Jiang ◽  
Zhi Gao Huang
Keyword(s):  
Magnetic Field ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Relaxation Time ◽  
Monte Carlo Method ◽  
External Magnetic Field ◽  
Low Temperature ◽  
Exchange Bias

The influnence of the amplitude (H0) and frequency of sweeped magnetic field on the exchange bias He and coercivity Hc for ferromagnetic/ antiferromagnetic films has been simulated with Monte Carlo method. In a cycle, the sweeped frequency is inversely proportional to Monte Carlo steps (MCSs). It is observed that, for smaller MCSs, the values of He and the blocking tempreture Tb reduce evidently with increasing MCSs; for larger MCSs, the values of He and Tb decrease gently with increasing MCSs. It is also found the values of He and Tb decrease obviously with increasing values of H0 (HN0). However, on the contrary, the value of Hc increases with increasing values of H0 (HN0). At low temperature and little HN0, the asymmetric loop may appear, which is attributed to the competition between the relaxation time and the period of the external magnetic field. Moreover, the symmetry of the loops influences evidently the values of He and Hc.

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