We report on the effect of agglomeration forced by strong electric field in fine particles of nearly ferroelectric YBa2Cu3O7-d superconductor. It turns out that the particles from agglomerates exhibit different morphology than the rest of powder that
attaches to high-voltage electrodes. Study by means of electron paramagnetic resonance revealed in the powder attached to electrodes a narrow spectrum superimposed on Cu2+ anisotropic spectrum common for YBa2Cu3O7-d superconductors. We assume that this narrow spectrum originates from nanopolar regions generated by strong electric discharges taking place during the experiment. Consequently, the effect of agglomeration can be explained in terms of electrostatic interactions between the particles containing nanopolar regions with strong electric dipolar moments.
This study reports on the synthesis of ball-like bismuth ferrite BiFeO3 nanoflowers by means of microwave assisted hydrothermal process and also on their composition and mechanism of growth. It turns out that the petals of the nanoflowers are compose
d of the nanocrystals with the size about 35-39 nm whereas their thickness and size depends on the concentration of surfactants. The petals contain BiFeO3 phase and traces of Bi2O3 oxide and metallic Bi and Fe deposited mainly at their surface. Amounts of impurity phases are more pronounced in nanoflowers synthesized during short time, and become almost negligible for longer microwave processing. The nanoflowers contain also mixed Fe valence, with the Fe2+/Fe3+ ratio depending on the time of synthesis. The growth and shape of the nanoflowers result from the process of diffusion in the initial stages of hydrothermal reaction.
The process of magnetic relaxation was studied in bismuth ferrite BiFeO3 multiferroic micro-cubes obtained by means of microwave assisted Pechini process. Two different mechanisms of relaxation were found. The first one is a rapid magnetic relaxation
driven by the domain reorientations and/or pinning and motion of domain walls. This mechanism is also responsible for the irreversible properties at low temperatures. The power-law decay of the magnetic moment confirms that this relaxation takes place in the system of weakly interacting ferromagnetic or superferromagnetic domains. The second mechanism is a longterm weak magnetic relaxation due to spin glass-phase.
In this report we present results of magnetization measurements and investigation of aging and memory effect in bismuth ferrite multiferroic micro-cubes obtained by means of simple microwave synthesis procedure. It is found that difference between FC
and ZFC magnetizations appears at the temperature of freezing of ferromagnetic domain walls. The decay of the magnetic moment vs. time described by power-law relation and the absence of memory effect indicate domain growth mechanism rather than the spin-glass phase.
