The second order phase transitions in spin systems

Ji-Xuan Hou, Xu-Chen Yu

The long-range interacting spin-1 chain placed in a staggered magnetic field is studied by means of microcanonical approach. Firstly, we study the microcanonical entropy of the system in the thermodynamic limit and find the system is non-ergodic and can exhibit either first-order phase transition or second-order phase transition by shifting the external magnetic field strength. Secondly, we construct the global phase diagram of the system and find a phase transition area in the phase diagram corresponding to the temperature jump of the first-order phase transition.

Alain H. Billoire

Johannes Richter, S E Kreuger, DAMIAN J. J. FARNELL +1 more

Cao Hai-xia

The spin-1 Ising system with bilinear and biquadratic interactions has been studied by the combination of the quantum statistical mechanics with the two-spin cluster approximation in face-center-cubic lattice. By use of the Qnsager theory, The behaviors of the spin-1 system such as the relaxation times, the sound attenuation were obtained near the second-order phase transition.

van Kah Ton Leeuwen

Akai Kurbanovich Murtazaev, I. A. Favorskii

First- and second-order phase transitions in the isotropic Heisenberg model with multispin exchange were investigated with the help of the quantum Monte Carlo method. The calculations were performed for a system with spin S = 1/2 and N = L3 spins (L = 8, 12, and 16) on simple cubic lattices with periodic boundary conditions. A relation between the pair and multispin exchange constants for which the second- order phase transitions are replaced by first-order phase transitions is established. First-order phase transitions have not been studied previously by the quantum Monte Carlo method. Phase diagrams were constructed for the model under study. The computational results are compared with the method of Green’s functions and the molecular-field theory.