Rojas M, Rojas Onofre, de Souza S M
Departamento de Ciencias Exatas, Universidade Federal de Lavras, CP 3037, 37200-000 Lavras, Minas Gerais, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Nov;86(5 Pt 1):051116. doi: 10.1103/PhysRevE.86.051116. Epub 2012 Nov 16.
Through the direct decoration transformation approach, we obtain a general solution for the pentagonal Ising model, showing its equivalence to the isotropic free-fermion eight-vertex model. We study the ground-state phase diagram, in which one ferromagnetic (FM) state, one ferrimagnetic (FIM) state, and one frustrated state are found. Using the exact solution of the pentagonal Ising model, we discuss the finite-temperature phase diagrams and find a phase transition between the FIM state and the disordered state as well as a phase transition between the disordered state and the FM state. We also discuss some additional remarkable properties of the model, such as the magnetization, entropy, and specific heat, at finite temperature and at its low-temperature asymptotic limit. Because of the influence of the second-order phase transition between the frustrated and ferromagnetic phases, we obtain surprisingly low values of the entropy and the specific heat until the critical temperature is reached.
通过直接装饰变换方法，我们得到了五角伊辛模型的一般解，表明它与各向同性自由费米子八顶点模型等价。我们研究了基态相图，其中发现了一个铁磁（FM）态、一个亚铁磁（FIM）态和一个受挫态。利用五角伊辛模型的精确解，我们讨论了有限温度相图，并发现了FIM态与无序态之间以及无序态与FM态之间的相变。我们还讨论了该模型在有限温度及其低温渐近极限下的一些其他显著性质，如磁化强度、熵和比热。由于受挫相和铁磁相之间二阶相变的影响，在达到临界温度之前，我们得到了出奇低的熵和比热值。
