Many problems in statistical physics resist exact solution once the number of interacting particles becomes large, and the two-dimensional Ising model is a classic case where numerical simulation fills that gap. This paper reports a Monte Carlo study of the two-dimensional Ising model using the Metropolis algorithm, undertaken to examine how magnetization, internal energy, specific heat, and magnetic susceptibility change with temperature. Spin configurations were generated on a square lattice under periodic boundary conditions, with each proposed spin flip accepted or rejected according to the Boltzmann weight of the resulting energy change. The simulation reproduces the expected transition from an ordered ferromagnetic state at low temperature to a disordered paramagnetic state at high temperature, with magnetization falling sharply and both specific heat and susceptibility peaking near a critical temperature of Tc ≈ 2.3–2.4 (in units of J/kB), consistent with the exact value obtained analytically for this system. These results confirm that the Metropolis algorithm, despite its simplicity, remains a dependable tool for locating second-order phase transitions and extracting thermodynamic quantities in lattice spin systems, and the same computational framework can be adapted to more elaborate models used in condensed matter and materials research.
We have studied the thermodynamic and magnetic properties of the spin 1/2 XXZ Ising model on a two dimensional square lattice using Monte Carlo simulation, in the presence of transverse magnetic field for varying lattice sizes (N=8-40) and exchange interaction strengths. The variations in specific heat and susceptibility for different N values is almost negligible, except for N=8. Interestingly, the magnetization showed large variation with N. This could be attributed to the increase in the disorder of spin alignment with increasing N.
Using the Monte Carlo Simulation (MCS) method combined with the Metropolis algorithm, we explore the magnetic properties of a two-dimensional (2D) spin system with spins 1, 2 and 3. The adapted simulation to the Ising model aims to study the impact of the correction term a of the interaction with second neighbors and the crystal field D on the critical temperature [Formula: see text] of the 2D anisotropic square lattice for different integer values of spins. The obtained results demonstrate that the critical temperature [Formula: see text] is significantly affected by the competing interactions between the anisotropy parameter, second-neighbor interaction and the crystal field. The considered model exhibits a critical phase transition regardless of the spin S value where the critical temperature increases with the value of S. Note that this phase transition occurs under the condition [Formula: see text]. Moreover, the obtained results show that the complex interactions give rise to a variety of phase diagrams, thereby revealing the richness of possible magnetic behaviors in the studied system.
The magnetic behavior of the spin-1/2 Heisenberg antiferromagnet on the extended Lieb lattice is examined in the presence of an external magnetic field. Using density matrix renormalization group calculations, we determine the zero-temperature magnetization curves and construct the ground-state phase diagram in the magnetic field vs. the interaction ratio plane. Depending on the interaction ratio, the zero-temperature magnetization curves exhibit field-driven quantum phase transitions between the gapped phases manifested as the intermediate plateaus at
1/5 and
3/5 of the saturation magnetization and a gapless spin-canted phase, in which the magnetization varies continuously with the applied magnetic field. Quantum Monte Carlo simulations reveal clear finite-temperatures signatures of the field-induced quantum phase transitions and the intermediate magnetization plateaus, while they provide no evidence for either continuous or discontinuous thermal phase transitions.
The authors have investigated the static critical behavior of a two-dimensional decorated Ising model on a square lattice in an external magnetic field, using computational physics methods. Particular consideration has been given to a special case when antiferromagnetic exchange interaction is observed only between decorated spins and spins located at lattice sites. It has been shown that at an external magnetic field of H0 = 4, the model experiences partial degeneracy in the ground state. At field values close to H0 = 4, heat-capacity splitting is observed.
We generalize a class of Heisenberg antiferromagnets in one, two, and three dimensions, which have been shown to exhibit magnetization plateaus for spin-
21. In a certain parameter range of the general model, which is formally defined in
D dimensions, we obtain the exact ground state(s) in the presence of an external magnetic field for arbitrary values of spin. In this range, the magnetization remains a constant as a function of the external field, except at some special values of the field where there is a jump from one plateau to the next. The plateaus are formed at certain specific fractions of the full magnetization which are determined by the spin and the lattice. Our general spin-
S result reproduces the known cases for spin-
21 in various lattices. Furthermore, we argue that outside the exact regime, the mechanism for the plateau formation is different. This results in first order phase transitions along some of the plateaus as the coupling constant is varied. We rigorously show the existence of such transitions for some particular cases. Finally, we numerically analyze a spin-
1 model in one dimension using exact diagonalization to obtain its complete phase diagram. It agrees with our analytic results.