Journal of Petrochemical Universities
The Ground-State Magnetic Properties of the Single-Ion Anisotropy Ising Model in Transverse Field
Jie Zhao, XU Xing-guang, Guozhu Wei
Abstract
The spin-2 Ising model with singleion anisotropies was studied in the transverse magnetic field.Using the mean-field theory,based on Bogoliubov inequality and used the Gibbs free energy as standard,the theoretic expressions of ground-state magnetic moment and free energy of system were deduced.The influences of single-ion anisotropy D and transverse field Ω on the magnetization and free energy curves of spin system at ground state were mainly explored and the characteristic of first order and second order phase transition was observed from magnetization curves.It is found that there are three kinds of magnetization curves with the change of single-ion anisotropy and the trans-verse magnetic field: first,the magnetic moment of the Ising system suddenly decreases from 2 to 1,which exhibits first order-order phase transition;second,the magnetic moment suddenly changes from 2 or 1 to 0,which exhibits first order-disorder phase transition;third,the magnetic moment smoothly changes from 2 or 1 to 0,which exhibits second order-disorder phase transition.The results show that first order-order (2-1),first order-disorder(1-0) phase transitions disappear one after another with the increasing of transverse field Ω in the m-D/(zJ) ground state magnetization curves.At the same time first order-order(2-1),first order-disorder(1-0) phase transitions also disappear in the same way with the increase of the single-ion anisotropy D in the m-D/(zJ) ground state magnetization curves.It is also found that the free energy always decreases when Ω or D increases through analysis of free energy curves at ground state.