Light-induced changes in the coercivity ΔHc are reported for cobalt ferrite nanoparticles. These changes arise from charge transfer initiated by optical absorption near 2 eV. An insulator-to-metal transition at 170 K is an upper limit for significant ΔHc. The larger ΔHc for smaller (17 nm) particles was correlated with a distortion about the Co2+ ions at B sites, which increases the absorption probability.

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Metal-polymer nanocomposites in the system iron-polyethylene have been prepared by high energy ball milling. Minimum average grain size obtained is of the order of 9 nm. Enhanced coercivity of 230 Oe at room temperature and 510 Oe at 5 K have been obtained for the sample containing 0.1 volume fraction of iron in polyethylene after milling for 200 h. This high value of the coercivity could be ascribed to the presence of a fraction of single-domain particles in the sample as evidenced from the thermal dependence of the magnetization and ac susceptibility measurements.

The process of mechanical milling of amorphous precursors can be used to produce bulk quantities of material with fine crystalline nanostructures. Here, the process and the factors which influence the quality of the materials produced are reviewed. The crystallization induced by mechanical milling and thermal annealing are compared and it is suggested that the induction of crystallization by ball milling may be a promising technique for preparing soft magnetic materials in powder form.

The stability of the Frohlich bipolaron in the strong-coupling limit is studied in both two and three dimensions using the Feynman-Haken path-integral method and the Landau-Pekar formalism.The ground-state energy, the effective mass, and the size of the bipolaron are obtained, and its stability criteria are predicted. The role of Coulomb correlation is also studied.The bipolaron problem has continued to remain a focus of attention, ' both for academic reasons and for its importance in semiconductor technology. Recently, however, research in this area has received some renewed impetus in the wake of the discovery of high-temperature superconductivity in CuOz-based layered ceramic materials. It has been advocated that the bipolaronic mechanism could also be a potential candidate for inducing superconducting pairing in these materials.