No abstract

γ − F e2O3 prepared by sol gel process was used to produce nanocomposites with polyaniline of varying aniline concentrations. TEM shows the presence of chain like structure for lower polyaniline concentration. The room temperature hysteresis curves show finite coercivity of ∼ 160 Oe for all the composites, while the saturation magnetization was found to decrease with increasing polymer content. ZFC -FC magnetization measurements indicate high blocking temperatures. It is believed that this indicates a strongly interacting system, which is also shown by our TEM results. Monte Carlo simulations performed on a random anisotropy model with dipolar and exchange interactions match well with experimental results.

The coupled double quantum dot system is modeled by a two impurity Anderson-type Hamiltonian and interdot Coulomb interaction is included. The conductance of this system is calculated using a nonequilibrium Green's-function formalism. We have evaluated conductance, peak splitting, and amplitude of conductance peaks as a function of Fermi energy for various values of parameters of the model Hamiltonian. It is demonstrated that an interdot interaction whose strength is assumed to be 10% of the ondot Coulomb interaction produces significant changes in the conductance in a coupled double quantum dot system.

No abstract

Iron oxide nanoparticles were prepared by sol -gel process. In-situ polymerization of pyrrole monomer in the presence of oxygen in iron oxide -ethanol suspension resulted in a iron-oxide polypyrrole nanocomposite. The structure and magnetic properties of the nanocomposites with varying pyrrole concentrations are investigated. The X-Ray diffraction studies indicate the presence of γ − F e 2 O 3 phase for the concentrations investigated. FTIR studies confirm the presence of polypyrrole. The TEM studies show agglomeration in uncoated samples and in samples with a lower concentration of polypyrrole. Agglomeration is much reduced for samples coated with higher concentration of polypyrrole. The ac susceptibility measurements performed in the temperature range 77 -300 K shows the presence of blocking, indicating the superparamagnetic phase. The blocking temperature is found to depend on the pyrrole concentration. Monte Carlo studies for an array of polydispersed single domain magnetic particles, based on an interacting random anisotropy model were also carried out and the blocking temperatures obtained from the simulation of the ZFC-FC magnetization compares favorably with experimental results.