具有Fe_4N结构的最近邻Ising模型相变的研究

Phase Transitions of Ising Model in Nearest Neighbor Interaction With Fe_4N Structure

对具有Fe4N结构的Ising模型,采用平均场理论,推导出考虑最近邻相互作用下系统的磁矩和自由能公式,并由数值计算方法,给出了为定值时的磁化曲线及相变曲线,得到了系统的相变特征。研究发现二级相变普遍存在,一级有序—有序相变、一级有序—无序相变及重入现象只存在于一定的晶场范围内,相图中重入现象、一级有序—无序相变、一级有序—有序相变对应的曲线相交于一点。相图中的低温相变特征与基态相图完全吻合。

The Ising model with Fe4 N structure was studied within the mean--field theory. The theoretic expressions of magnetization and free energy in the nearest neighbor interaction system were deduced. The magnetization curves and phase diagrams were given at a fixed value of through numerical calculation, and the phase transition characteristics were obtained. It was found that the second--order phase transitions were general phenomena, and the first order--order, the first order-- disorder phase transitions and reentrant phenomena only exist in a certain range of crystal field. In the phase diagram the curves of reentrant phenomena, the first order--order and the first order--disorder phase transitions intersect at one point. It was found that the phase transition characteristics in the phase diagram at low temperature are completely consistent with the characteristics in the ground--state phase diagram.