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The composite material made of biodegradable chitosan as a matrix and spinel CoFe2O4, exhibiting the ferrimagnetic properties, was proposed to be suitable for application in modern transducers, for instance in a loudspeaker without a permanent magnet. The spinel was obtained by high-energy ball milling followed by annealing. The composites were prepared by the solvent casting method. The dielectric studies using broadband impedance spectrometer and the applied methodology of subtracting the conductivity term from the dielectric absorption spectra pointed to the presence of two low-frequency relaxations in chitosan as well as in the composites: α - related to the glass transition (310-350 K), and σ - related to the migration of protons (350-420 K). In the high frequency range, the secondary β-relaxation, related to side group motions by means of the glucosidic linkage, was observed in the temperature range 300-350 K. However, for the composite samples, additionally, the process associated with the migration of oxygen vacations in the spinel grains was detected within the temperature range 350-380 K. One can notice a significant decrease in the activation energy of all processes with increasing contents of spinels in the chitosan matrix. [ABSTRACT FROM AUTHOR]

Novel, flowerlike bismuth ferrite BiFeO3 (BFO) multiferroic structures were prepared for the first time by means of microwave assisted hydrothermal synthesis. The flowers are composed of numerous petals formed by BFO nanocrystals and some amount of amorphous phase. The growth of the flowers begins from the central part of calyx composed of only few petals toward which subsequent petals are successively attached. The flowers exhibit enhanced magnetization due to size effect and lack of spin compensation in the spin cycloid. The dielectric properties of the flowers are influenced by BFO amorphous phase resulting in a broad dielectric permittivity maximum at 200-300 K and also by Polomska transition due to anomalous surface magnon damping above the temperature of 450 K. Possible applications of BFO flowerlike structures assume optoelectronic devices, excellent field emitters, effective solar cells, or catalyst supports. [ABSTRACT FROM AUTHOR]