Monte Carlo Study Of The3D Mixed Spins System In External Magnetic Field

In recent years, much attention has been paid to the mixed-spin systems. In this thesis, westudy the physical properties of spin-1and spin-3/2mixed Ising ferromagnetic model on simplecubic lattice with crystal field interaction as well as external magnetic field interaction. The maincontents of the thesis are as following.Firstly, we have briefly reviewed the history of Ising model, then discussed the exactsolutions of one-dimensional and two-dimensional Ising model as well as the approximatesolution of the three-dimensional Ising model.Secondly, we have introduced the basic principles of Monte Carlo method, and discussed itsapplications to the study of spin-lattice systems.Thirdly, we have studied the physical properties of spin-1and spin-3/2mixed3D Isingferromagnetic system with crystal field interaction as well as external magnetic field interaction.Magnetization M, magnetic susceptibility χ, energy E and specific heat C as a function oftemperature, crystal field and external magnetic field for different parameters have beencalculated. The obtained results are shown as follows, magnetization decreases with theincreasing of temperature. The system can be in different magnetic order phases for appropriatevalues of the single-ion crystal fieldD_AandD_B. The order-disorder transition criticaltemperature of the system in the case of existing external magnetic field is higher than that in thecase of no external magnetic field, that is to say that the system in the external magnetic field cankeep the magnetic order state at higher temperature. Magnetization decreases in setback typewith the increasing of the crystal field, compared with the case of no external magnetic field, thenumber of order phases increases in the external magnetic field, which may be related to theremoval of the degeneracy of energy. Magnetization increases in setback type with the increasingof the external magnetic field, the magnetic field ranges for maintaining each order phasebecome larger with the increasing of crystal field. On the relationship between magneticsusceptibility and temperature, the peaks of the curve move to the left with the increasing ofcrystal field, that is to say that higher crystal field makes the transition critical temperaturedecrease. On the relationship between magnetic susceptibility and crystal field, the peak of thecurve moves to the right in the case of existing external magnetic field compared with the case ofno external magnetic field, that is to say that external magnetic field makes the critical crystalfield for phase transition increase. On the relationship between magnetic susceptibility and theexternal magnetic field, the peaks of the curve move to the right with the increasing of the crystalfield, that is to say that higher crystal field makes the critical magnetic field for phase transition increase. On the relationship between energy and temperature, the energy of the order phasereduces with the increasing of the crystal field. When the temperature is lower than phasetransition temperature, the energy reduces rapidly with the increasing of temperature; when thetemperature is higher than phase transition temperature, the energy increases slowly with theincreasing of temperature. On the relationship between system energy and the crystal field,within the same order phase the energy increases linearly with the increasing of the crystal fieldwhether the external magnetic field exists or not. Energy increases in setback type with theincreasing of the external magnetic field, within the same order phase the energy does not changewith the increasing of the external magnetic field and increases slightly with the increasing of thecrystal field. On the relationship between specific heat and temperature, the peak of the curvemoves to the right in the case of existing external magnetic field compared with the case of noexternal magnetic field, the system in the external magnetic field can keep the magnetic orderstate in higher temperature, and meanwhile the phase transition process become indistinct. Onthe relationship between specific heat and crystal field, a new order phase emerges in theexistence of the external magnetic field compared with the case of no external magnetic field.Specific heat increases in setback type with the increasing of the external magnetic field, it doesnot change with external magnetic field within the same order phase. With the increasing of thecrystal field, the critical external magnetic field for a new order phase emerging increases.