Improved effective field theory analysis of critical phenomena in Ising model with quenched disorder effects

This thesis report is essentially based on the results of recent series of papers concerning the critical phenomena and order-disorder phase transition characteristics of Ising model and its various generalizations in the presence of several kinds of quenched disorder effects. In order to investigate the magnetic properties of aforementioned models, we have proposed a formalism based on the effective-field theory (EFT) which improves the results provided by conventional EFT approximations in the literature by systematically including the multi-site, as well as single-site spin correlation functions in the calculations within a heuristic manner.Numerical computations are performed and the results are analyzed for the cases of spin-1 Blume-Capel model in the presence of longitudinal and transverse magnetic fields (Yüksel & Polat, 2010), site diluted Ising ferromagnets (Akinci, Yuksel, & Polat, 2011c), bond diluted spin-1 Blume-Capel model with transverse and crystal field interactions (Akinci, Yuksel, & Polat, 2011b), spin-1 Blume-Capel model with random crystal field interactions (Yüksel, Akinci, & Polat, 2012a), and Ising model in the presence of random magnetic fields (Akinci, Yuksel, & Polat, 2011a).