Double-exchange Model And The Spin Glass Monte Carlo Method

The doped manganese oxides, widely known as manganites, that exhibit the "Colossal" Magnetoresistance (CMR) effect, have been a main focus of condensed matter physics researches in recent years owing to the potential applicability as well as fascinating phase diagrams. The theoretical and experimental studies suggest that the ground states of manganite models tend to be inhomogeneous due to the presence of strong tendencies toward phase separation. The double exchange model with antiferromagnetic coupling for localized spins is proposed to qualitatively explain the stability of the antiferromagnetic state and phase separation near x = 0 or 1. The internal energy, the electron density as a function of chemical potential and the structure factor are computed by using Monte Carlo simulations. The phase diagram is drawn with the information about these observables. The thermodynamic properties also calculated for different phase and low temperature properties at quarter filling are studied in details.Spin glasses are materials whose magnetic properties are strongly influenced by disorder and frustration. For two Archimedean lattices, (3,12~2) and Kagome lattices, the frustration is already incurred by their structure with antiferromagnetic coupling between two Ising spins in each nearest neighbor pair. The internal energy, specific heat, free energy, entropy, magnetization, and spin susceptibility are calculated by using Wang-Landau algorithm of the Monte Carlo simulation.Diluted magnetic semiconductors (DMS) are attracting much attention lately due to their potential for device applications in the growing field of spintronics. Their dynamical and transport properties are strongly influenced by disorder. A simple single impurity band spin-fermi lattice model is discussed using Monte Carlo simulations. The density of states and optical conductivity are calculated.