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Investigation of the Low Frequency Polarization Mechanisms in Magnetic Fluids

100%

Marin C., Malaescu I., Savici A.

Acta Physica Polonica A

2013

vol. 124

issue 4

724-727

The dielectric behaviour of a magnetic fluid with magnetite particles dispersed in kerosene was analyzed. Therefore, the frequency (f) and temperature (T) dependences of the complex dielectric permittivity, ε (f, T), over the ranges 4 kHz to 2 MHz and 25C to 90C were measured. Based on the experimental results of ε (f, T) and using the Clausius-Mossotti equation, we have determined the temperature dependence of the real part of the total polarizability α', of a magnetic fluid. The computations have taken into account that the magnetic fluid consists of three components, namely magnetite particles, surfactant, and carrier liquid. The results show that at a given frequency, α' increases with temperature in the low frequency range (4 kHz to 100 kHz) and decreases with temperature above 100 kHz. This behaviour demonstrates that in low frequency range the polarization mechanism related to the deformation of the counter ions atmosphere around each particle is predominant and above 100 kHz the orientation of the dipole moments is the main polarization mechanism of the magnetic fluid. These measurements enabled the evaluation of the effective dipole moment of the magnetic fluid, in order of 1.21 × 10^{-30} C m.

The Electrical Properties of Some Composite Materials Based on Sodium and Tantalum Oxides

88%

Malaescu D., Grozescu I., Sfirloaga P., Vlazan P., Marin C.

Acta Physica Polonica A

2016

vol. 129

issue 1

133-137

Two samples of Na-Ta oxides were synthesized by the hydrothermal method at reaction temperatures of 160°C (sample A) and 200°C (sample B). For reference, a third sample of pure NaTaO₃ was prepared by the sol-gel method (sample C). Using X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectra and electric measurements, structural, morphologic, spectroscopic and electric properties of samples were investigated. The structural characterization by X-ray diffraction revealed that samples A and B are mixtures of Na-Ta oxides (including NaTaO₃ and other compounds), whilst sample C is pure NaTaO₃. UV-vis diffuse reflectance spectra allowed evaluation of the band gap energy (E_{g}), resulting in 3.88 eV for sample A, 3.93 eV for sample B and 4.1 eV for sample C. Electrical resistivity measurements, over the temperature range 300-450 K, showed a typical semiconductor behavior of the investigated samples, with the effective activation energy, E_{a} of 0.47 eV (sample A), 0.45 eV (sample B) and 0.82 eV (sample C). Based on the Mott variable range hopping model, the conductivity mechanism in the investigated samples was analyzed. The results shown that the density of states at the Fermi-level, N(E_{F}) is constant in the investigated temperature range and the typical values of N(E_{F}) are 0.713 × 10^{18} eV^{-1} cm^{-3} (sample A), 0.621 × 10^{18} eV^{-1} cm^{-3} (sample B) and 0.855 × 10^{17} eV^{-1} cm^{-3} (sample C). Other parameters of VRH model such as the hopping distance R and the hopping energy W have also been computed and the following values at the room temperature were obtained: R=15.7 nm and W=86 meV (for sample A); R=16.3 nm and W=89 meV (for sample B) and R=26.7 nm and W=147 meV (for sample C).

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2 Acta Physica Polonica A

1 2016

1 2013

2 Marin C.

1 Grozescu I.

1 Malaescu D.

1 Malaescu I.

1 Savici A.

1 Sfirloaga P.

1 Vlazan P.

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Investigation of the Low Frequency Polarization Mechanisms in Magnetic Fluids

The Electrical Properties of Some Composite Materials Based on Sodium and Tantalum Oxides