Magnetically induced dielectric anisotropy in concentrated ferrofluids

Abstract

Magnetically induced dielectric anisotropy (MDA) has been studied in concentrated suspensions of magnetite in paraffin (n-hexadecane). The volumetric fraction was phi =0.3. The maximum value for the applied magnetic field was 48 kA m-1. A clear trend to the saturation in MDA was found for applied fields larger than 32 kA m-1. In this case, the dielectric anisotropy is up to 15% of the dielectric constant at zero field. A constant value for g=1.23 was found for magnetic fields higher than 12 kA m-1 (g=( epsilon /sub ///- epsilon (0))/( epsilon (0)- epsilon perpendicular to ) where epsilon (0) is the dielectric constant at null field). Below this field, a transition to g=1 was attained at 4 kA m-1. These results disagree with the value g=2 theoretically deduced for ideally monodispersive suspensions in the overall field range. The present results are tentatively explained qualitatively and quantitatively taking into account the mechanism of particle aggregation.

Magnetodielectric Properties of Transformer Oil Based Magnetic Fluids

“…The induced anisotropy in relative permittivity of a magnetic uid subjected to an external magnetic eld can be seen. The magnetodielectric anisotropy factor g(B, ω) calculated according to formula (1) is very close to value g = 1 for all volume concentrations which is in agreement with formerly published results [1].…”

“…Experimentally, Cotae [5] and Espurz et al [1] have obtained the value of 1 for g(H, ω) while Mailfert and Nahounou [2] have obtained a value of 2. Experimental results of Espurz et al [1] show that the value of g(H, ω) is 1 at low elds and 1.23 at high elds. The present work is devoted to studying the dielectric and magneto-dielectric properties of transformer oil based magnetic uids depending on concentration of magnetite nanoparticles and mutual orientation of magnetic and electrical elds.…”

“…The dielectric behavior of magnetic uids changes with the application of an external magnetic eld and with the relative orientation of the electric and magnetic elds. This eect is known as magneto--dielectric anisotropy eect [1].…”

“…Measurements of the impedance parameters such as the modulus and phase are carried out using a bridge or an RLC meter. The impedance measurement techniques suer some serious disadvantages such as electrode effects, parasitic impedances, skin depth and accuracy related problems, but the works [1,7] have determined the magneto-dielectric eect from magneto-optical measurements where the disadvantages suered by conventional impedance measurement techniques are avoided.…”

“…The value of g was either 2 or 1 [810]. Experimentally, Cotae [5] and Espurz et al [1] have obtained the value of 1 for g(H, ω) while Mailfert and Nahounou [2] have obtained a value of 2. Experimental results of Espurz et al [1] show that the value of g(H, ω) is 1 at low elds and 1.23 at high elds.…”