关键词: 平均场理论 , 混自旋 , 基态相图 , 磁化曲线 , 重入现象

Abstract: When the crystal field exists, the mixed spin Ising model in nearest neighbor interaction with Fe4N 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 influences of the nearest interactions and the crystal field on the magnetic properties were mainly explored. The ground-state phase diagram and magnetization curves in finite temperature were obtained. Abundant phase transition characters were observed in the system: reentrantant phenomena, and second-order phase transitions. It is found that second-order phase transitions are general phenomena, and second-order phase transitions must exist in the system when DA/|J1| and DB/|J1| get the adequate large values. On the boundary lines of D1 to O1and D2 to O1、O2 reentrantant phenomena may occur.

Key words: Mean-filed theory , Mixed spin , Ground-state phase diagram, Magnetization curve, First-order phase transition, Reentrantant phenomena