关键词: 平均场理论 , 内能 , 相变潜热 , 比热 , 一级相变

Abstract: Using the mean-field theory, numerical calculation expressions for the internal energy and specific heat were obtained, within the BC model considering the transverse high spin S=2 ferromagnetic system. The thermodynamic properties were investigated mainly nearby the phase transition points of the system, especially nearby the first-order phase transition points. The longitudinal crystal field dependence of the thermodynamic properties in the system was explored. It is found in the system that there is latent heat of phase transition only in very small crystal field range and the corresponding specific heat decrease suddenly, namely the first-order phase transition appears when the transverse field remains the same value. Then with the increase of crystal field, there is no hidden heat of phase transition in the system, the internal energy changes continuously and the corresponding specific heat suddenly decreases, namely the second-order phase transition appears. When the first order-order phase transition appears specific heat increases suddenly and when the second-order phase transition appears specific heat decreases suddenly. With the decrease of crystal field the internal energy increases and the specific heat decreases within the second-order phase transition range. The internal energy and the specific heat vary complexly within the first-order phase transition range.

Key words: Mean-field theory , Internal energy , Latent heats of phase transition , Specific heat , First-order phase transition 