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This work used Monte Carlo simulation to investigate the effect of lattice strain on critical temperature of the ferromagnetic Ising ultra-thin-film. Using Bethe-Slater interpretation, exchange interaction was assumed Lennard-Jones (LJ) potential function, and becomes functions of interatomic distance. The cluster flip algorithm was used to update the spin configuration, where energy and magnetization were measure to extract critical temperature via the fourth order cumulant of the magnetization. Results show that initial interatomic distance and strain have strong effect on magnetic critical point behavior. The critical point can be enhanced or suppressed depending on how exchange interaction is modified by the values of initial interatomic distance and strain. A scaling function in predicting critical temperatures is also given in this work. Results agree well with previous applicable works, which confirms the reliability of the reported results.

This work studies the temperature-driven ferroelectric phase transition of ferroelectric polarization under the absence of electric field. The modified Heisenberg model in three dimensions was considered and simulated via Monte Carlo simulation. The Metropolis algorithm and the periodic boundary condition were employed. The dependence of electric polarization on temperature was investigated to define the ferroelectric phases and their structural phase transitions. From the results, with well-defined set of relevant temperature parameters, the phase dependent polarization-behavior was found with a sudden change in its behaviors at the transition points. The structure factors were also considered and supported these phase changes. This conclusively pinpointed the important of temperature-dependent parameters in modeling ferroelectric materials.

This work used Artificial Neural Network (ANN) to investigate the hysteresis behavior of the Ising spins in structures ranging from one-to two-and three-dimensions. The equation of magnetization motion under the mean-field picture was solved using the Runge-Kutta method to extract the Ising hysteresis loops with varying the temperature, the external magnetic field parameters and the system structure (via the variation of number of nearest neighboring spins). The ANN was then used to establish relationship among parameters via Back Propagation technique in ANN training. With the trained networks, the ANN was used to predict hysteresis data, with an emphasis on the dynamic critical point, and compared with the actual target data. The predicted and the target data were found to agree well which indicates that the ANN functions well in modeling hysteresis behavior and its critical phase diagram across systems with different structures.

In this work, the Artificial Neural Network (ANN) was used to model ferroelectric hysteresis using data measured from soft lead zirconate titanate [Pb (Zr1−xTix)O3 or PZT] ceramics as an application. Data from experiments were split into training, testing and validation dataset. Four ANN models were developed separately to predict output of the hysteresis area, remnant, coercivity and squareness. Each model has two neurons in the input layer, which represent field amplitude and field frequency. The ANNs were trained with varying number of hidden layer and number of neurons in each layer to find the best network architecture with highest accuracy. After the networks have been trained, they were used to predict hysteresis properties of the unseen testing patterns of input. The predicted and the testing data were found to match very well which suggests the ANN success in modeling ferroelectric hysteresis properties obtained from experiments.

The scaling behavior of the dynamic hysteresis of ferroelectric BaTiO3 bulk ceramics was investigated. Two sets of the scaling relation of hysteresis area against frequency f and field amplitude E0 were clearly established. Approximately, above the coercive field, the scaling took a form of  f -0.23E00.87. On the other hand, the scaling in the form of  f -0.36E03.64 was obtained under a sub-coercive field condition. While these scaling relations were generally comparable to previously reported ones, it was found that the f- and E0 exponents clearly depended on E0 and f, respectively.

In order to investigate the mechanism of hybrid doped ferroelectric, BaTiO3 sample was prepared via conventional mixed-oxide method. The sample was then subjected to doping process with Fe3+ as acceptor dopant and Nb5+ as donor dopant. With varied concentration of acceptor dopant from 0.5 to 1 %M at fixed 1%M of donor, hysteresis property was obtained via Sawyer-Tower circuit. The hysteresis property of the sample was observed to vary over time by influence of ageing effect. By numerical scaling, the stretched exponential decay behavior of the system was obtained to gain the better insight of ageing mechanism of hybrid doped ferroelectric. With stretched exponential fitting, stretching parameter of lower doped Nb5+ were observed lower than that of equivalently doped Nb5+.

A 2D Monte Carlo simulation was done as an approach to get further insight of acceptor-doped ferroelectric material. By utilizing vector model allowing 14 directions of orientation for ferroelectric systems, Metropolis algorithm was applied on DIFFOUR Hamiltonian to obtain hysteresis profiles. Subjected to different concentration of acceptor dopants, power law scaling of hysteresis properties were obtained as functions of external parameters such as temperature, external field amplitude and frequency. The hysteresis loop shape and properties agreed well with those obtained experimentally.

In this work, we used Monte Carlo simulation to investigate the uniaxial stress dependence of the relaxor dielectric properties. The Metropolis algorithm and the spin glass type interaction were used in updating the local polarizations (representing the polar nano-regions). The exchange interaction in the spin glass Hamiltonian was assumed to be stress dependent via the strain. From the results, the frequency dependence of the dielectric permittivity were found, where, at high enough stress, the dielectric permittivity decreases with increasing stresses in qualitatively good agreement with experiments. In addition, from the modified Curie-Weiss law, all ’s stay close to 2. Therefore, this implies the frequency dispersion universality of the relaxor system under loading conditions.

In this work, the ferroelectric hysteresis in thin films was investigated with Monte Carlo simulation using the DIFFOUR Hamiltonian and the Metropolis algorithm. The field frequency, the filed amplitude and the thickness dependence of hysteresis properties were found. For instance, at high enough field, the area increases, maintains and reduces with increasing frequency. However, with increasing the film’s thickness, the area increases over the whole considered frequencies, and the frequency at maximum area shifts to a lower frequency due to the stronger ferroelectric coupling in thicker films. This strongly indicates the thickness dependence of the ferroelectric hysteresis. In addition, the power law scaling relation between the hysteresis properties and input parameters, which are the film’s thickness and the field parameters, were proposed. The scaling exponents were compared and discussed with previous investigations on thin ferroelectric films.

In this work, effects of compressive stress on the ferroelectric properties of 0.7PMN–0.3PT ceramics were investigated. The ceramics with the formula (0.7)Pb(Mg1/3Nb2/3)O3-(0.3)PbTiO were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress were observed at stress up to 80 MPa using a compressometer in conjunction with a modified Sawyer-Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of 0.7PMN–0.3PT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P-E) loop, the saturation polarization (Psat), the remanent polarization (Pr) and loop squareness (Rsq), decreased with increasing compressive stress, while the coercive field (Ec) remained relatively constant. Stress-induced domain wall motion suppression and non-180oC ferroelectric domain switching processes are responsible for the changes observed.

Monte Carlo simulation was used to observe the dynamic magnetic behavior of dilute Ising ultra-thin-film. The hysteresis properties were investigated as varying the non-magnetic concentration, field frequency and field amplitude where the Metropolis algorithm was used. From the results, at fixed temperature and field amplitude, the hysteresis loop increases in size with increasing frequency at low frequency region but reduces at high frequency region due to the increase of the phase-lag between magnetization and external field signals. With the inclusion of non-magnetic sites, the phase-lag shifts to higher frequency as a result of weaker magnetic interaction. In addition, the scaling relation among the hysteresis area, the field parameters and non-magnetic concentration was proposed to provide general information of how the dilution affects hysteresis properties of dilute magnetic in ultra-thin-film structure.

Effects of electric field-amplitude and mechanical stress on hysteresis area were investigated in partially depoled hard PZT bulk ceramic. At any compressive stress, the hysteresis area was found to depend on the field-amplitude with a same set of exponents to the power-law scaling. Consequently, inclusion of compressive stresses into the power-law was also obtained in the form of < A – Aσ=0 > α E05.1σ1.19 which indicated the difference of the energy dissipation between the under-stress and stress-free conditions.

The compositions of Pb(Zr0.52Ti0.48)O3 doped with 1-6 mole% Nb content were prepared by a conventional mixed oxide technique. It was found that the phase formed depended on the dopant concentration. At lower concentration, the dominate phase was the tetragonal. With increasing Nb content the rhombohedral phase tended to increase. Furthermore, the Curie temperature (Tc) and dielectric constant decreased with increasing Nb concentration and the dielectric maximum peaks were broadened with more rhombohedral phase presence, causing the diffused ferroelectric-paraelectric phase transition. The impedance of the samples decreased with increasing temperature and it was also observed that the impedance increased with increasing Nb concentration.