Monte Carlo study of compensation and critical temperatures in ferrimagnetic mixed Ising systems

In this thesis, three different mixed Ising model isstudied by using Monte Carlo simulation method. Since realferrimagnets have fairly complicated structures, mixed Ising spin models have been used as simple systems that can characterize ferrimagnetic behavior. Magnetic materials have been a very important part of our lives due to numerous technological applications such as memory devices. Especially, ferrimagnetism plays a key role in the physics behind magneto-optical recording.Therefore, in this thesis, three different mixed Ising model have been examined.In the first study, dependence on site dilution of critical andcompensation temperatures of a two dimensional mixed spin-1/2 and spin-1 system has been investigated. The dependence of the thermal and magnetic behaviors on dilution of mixed spin system have been discussed. The results of this study show that dilution plays a significant role on the critical and compensation points of a two dimensional mixed spin-1/2 and spin-1 system. It has been shown that the critical and compensation temperatures of diluted mixed spin system linearlydecrease with increasing number of diluted sites. Results of this study indicate that the compensation temperatureof the real ferrimagnetic spin systems can be changed by diluting the lattice with non-magnetic atoms, in order to obtain desired compensation temperature.In the second study, the compensation temperature of the mixedferro-ferrimagnetic ABpC1-p ternary alloy composed of threedifferent Ising spins SA=3/2, SB=1 and SC=5/2 in the presence of next nearest neighbor interaction JAA between A ions is studied in cubic lattice whose spin values corresponding tothe Prussian blue analog of the type (NipIIMn1-pII)1.5[CrIII(CN)6].nH2O (Okhoshi et al., 1997a). By changing concentration p and interaction parameter R, we obtain interesting properties of ferro-ferrimagnetic ternary compound.Results of in this work show that the system has multi-compensation behavior with suitable R, p and JAA parameters.In the third study, it has been investigated the effects ofsingle-ion anisotropy on magnetic properties of three dimensional mixed ferro-ferrimagnetic model consisting of three different Ising spins SA=3/2, SB=2 and SC=5/2 which corresponds to Prussian blue analog (FepIIMn1-pII)1.5[CrIII(CN)6]nH2O (Okhoshi et al., 1997a). It have been found that the critical temperature Tc of this system linearly changes dependent upon the interaction ratio R for any mixing ratio p value, and critical interaction Rc decreases for increasing D values. In addition, we have demonstrated that the magnetic pole inversion can appear and compensation temperature Tcomp decreases for increasing external magnetic field dependent upon some values of the Hamiltonian parameters. As a result, we state that single-ion anisotropy can be used as a control parameter like mixing rate p to arrange the critical and compensation temperature of the Prussian blue analog (FepIIMn1-pII)1.5[CrIII(CN)6].nH2O.