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AC Magnetic Susceptibility of Ferrofluids Exposed to an External Electric Field

100%
Rajňák M., Dolník B., Kováč J., Paulovičová K., Mitróová Z., Kurimský J., Cimbala R., Kopčanský P., Timko M.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
887-889
EN
It is known that ferrofluid superparamagnetic nanoparticles response to external magnetic fields, often resulting in the formation of elongated clusters along the field. This has a notable impact on dielectric properties of ferrofluids. Here we report on indications of a contrary effect when the magnetic susceptibility of ferrofluids based on transformer oil is influenced by an external electric field. This effect is associated with structural changes in the ferrofluids induced by the external electric fields. Particularly, we focus on a steady state electric field effect, which gives rise to forces acting on the magnetite nanoparticles, leading to the formation of aggregates. In this condition we have measured the ferrofluid AC magnetic susceptibility in parallel and perpendicular configuration of magnetic and electric fields at room temperature. The measurements in both configurations yielded a noticeable decrease in the real susceptibility values with increasing electric field intensity. The result is believed to be caused by the reduction in the total magnetic moment of the ferrofluid. This can be a consequence of the superspin interactions in the aggregates, minimizing the aggregate's energy. Finally, we highlight the necessity of NMR and small angle scattering of polarized neutrons investigations in order to obtain exact information on the magnetic structure induced by the electric forces.
2
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Microstructure and Dynamics of Magnetic Iron Nanoparticles Aggregates in Protein Gels

100%
Konik K., Fornal P., Okła D., Stanek J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
457-463
EN
The 60 nm metallic iron nanoparticles and its aggregates in gelatine gel were studied by means of optical microscopy, X-ray microtomography, atomic force scanning microscopy and the Mössbauer spectroscopy. The isolated nanoparticles in gel exhibit fast bounded diffusion described by Brownian movement. In the external magnetic field these magnetic particles form spectacular linear aggregates whose local dynamical and magnetic properties were determined from the Mössbauer spectra.
3
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Electro-Rheological Properties of Transformer Oil-Based Magnetic Fluids

100%
Paulovičová K., Tóthová J., Rajňák M., Timko M., Kopčanský P., Lisý V.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1141-1143
EN
The aim of this work was to study rheological behavior of nanofluids affected by electric field and temperature. We used transformer oil-based magnetic fluids, the suspensions of permanently magnetized colloidal particles (Fe_3O_4) coated by a stabilizing surfactant and immersed in transformer oil. The rheological characterization of transformer oil-based magnetic fluid was performed using the rotational rheometer MCR 502 in the shear rate from 10 to 1000 s¯¹.The strength of electric field was changed in the interval 0-6 kV cm¯¹. The flow curves and viscosity functions detected at three different temperatures 25, 50, and 75°C disclose rheological characteristics of samples, first of all the viscosity growth under increasing strength of electric field.
4
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An Improvement of Magnetic Flux Linkage in Electrical Generator using the novel Permanent Magnet Arrangement

75%
Sriwannarat W., Khunkitti P., Janon A., Siritaratiwat A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
642-644
EN
The partitioned stator permanent magnet generator (PS-PMG) has been extensively used as electrical generator due mainly to their high flux linkage, high electromotive force EMF) and high efficiency, especially the PM arrangement of the PS-PMG is an important factor to improve the performance of the generator. Therefore, we propose the novel permanent magnet PM) arrangement of the PS-PMG by using the dual rotor with coaxial core structure in order to improve the flux linkage and the EMF of PS-PMG. The PM position of stators of the conventional PS-PMG was rearranged, then the electrical characteristic of the proposed structure was characterized through the simulations based on finite element method. It was found that the flux linkage produced by the proposed structure is 37.06% higher than that of the conventional PS-PMG existed in the literatures because the area for induced flux linkage is significantly increased. This flux linkage enhancement further causes an increment of EMF about 34.95% compared to that of the conventional PS-PMG under the same condition. Especially, the EMF produced by the proposed structure is classified in the high-value range regarding the PM generator. Then, the PS-PMG using novel permanent magnet arrangement could be another remarkable choice for the electrical generator application
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