Ac-susceptibility study in rare earth substituted magnetite ferrofluids

AbstractIt is shown that variation of the third order ac-susceptibility as a function of measuring field and frequency lead to distinguish between superparamagnetic and spin glass like ordering in the rare earth substituted magnetic ferrofluids. We observe the divergent behavior of the peak values of the third order susceptibility, as a function of measuring field and frequency, tends to zero is consistent with theoretical prediction for the ground state for a spin glass like system. This behavior is further substantiated by a linear dependence of log-log plots of peak of the third order susceptibility as a function of the measuring field and frequency

Magnetic fluid based separator: Design and development

319-322<span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">Salient features of a magnetic fluid based separator, which can be used to recover certain non-magnetic materials from waste materials like automobile scraps, industrial wastes, household electrical appliances, etc ., have been described. The magneto-hydrostatic separator is built using the phenomenon of levitation of non-magnetic objects submerged in a magnetic fluid when in influenced by a gradient magnetic field. A prototype model is fabricated in the laboratory, using permanent ferrite magnets. The detailed study about the geometry and requirement of properties of magnetic fluid are discussed. The test results of this model are also described. </span

Effect of preparative conditions on magnetic properties of CoFe 2 O 4 nanoparticles

Nanomagnetic particles of CoFe2O4 have been synthesized using chemical co-precipitation technique followed by annealing, characterized and investigated by powder XRD and magnetic measurement tools. All samples of nano ferrites synthesized at different annealing temperatures show single phase cubic spinel structure with particle size changes from 9.5 to 21 nm. The virgin curve of magnetic measurement exhibits superparamagnetic behaviour at room temperature which changes to 'S' shape with increasing annealing temperature indicating change in soft magnet to pinning-type magnet. The coercivity of the nano-cobalt ferrite particles has been found to increase with increase in annealing temperature.by Kinnari Parek

Thermomagnetic behaviour of Gd substituted ferrite magnetic fluids*

282-289<span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">Gd substituted Mn-Zn (50%) ferrite magnetic fluids have been synthesized to achieve a high value of pyromagnetic coefficient. Thermo-magnetic behaviour of the fluids are studied with the temperature, field and different concentrations of Gd. The results indicate that the substitution of Gd (2.5%) increases the particle size without altering its magnetic moment while on <span style="font-size: 15.0pt;mso-bidi-font-size:8.0pt;font-family:" times="" new="" roman","serif""="">further addition of Gd (5%) will increase the magnetic moment with the same particle size. It is also observed that Gd (5%) substituted sample has higher value of pyromagnetic coefficient compared to that of the parent system Mn-Zn (50%) ferrite and Gel (2.5%) substituted ferrite. </span

Magnetic field induced enhancement in thermal conductivity of magnetite nanofluid

Magnetite nanofluid is synthesized using continuous chemical process. Powderx-ray diffraction and transmission electron microscopy show single phase spinel structure with size of 9.83 and 9.9 nm, respectively. Thermal conductivity of magnetite nanofluid has been studied as a function of transverse magnetic field and temperature. We found almost 30% enhancements in thermal conductivity for 4.7% volume fraction under transverse magnetic field. This result is explained on the basis of formation of continuous three-dimensional zipperlike structure of magnetic nanoparticles inside magnetic fluid. The temperature dependent thermal conductivity shows no enhancement in the temperature region of 25–65 °Cby Kinnari Parekh and Hyo Sook Le

Static and dynamic magnetic properties of monodispersed Mn0.5Zn0.5Fe2O4 nanomagnetic particles

Static and dynamic magnetic properties of oleic acid/oleyamine coated Mn–Zn ferritenanoparticles of diameter 82 Å are reported. The zero-field-cooled peak temperature decreases with increasing magnetic field and obeys the well known de Almeida–Thouless line. The zero-field-cooled magnetization data are simulated by assuming noninteracting magnetic particles with uniaxial anisotropy and lognormal particle size distribution. The relevant parameters give the values of particle diameter (D) 80 Å, standard deviation 0.3 in ln(D), and the anisotropy constant K to be 5.8×105 erg/cm3. The observed higher value of standard deviation is due to the interparticle interaction. The complex magnetic susceptibility was measured as a function of temperature for frequencies ranging from 67 to 1800 Hz. The temperature at which the maximum in the ac-susceptibility curve is observed is well accounted by the Vogel–Fulcher law for both χ′ and χ′′. The peak is also observed in a plot of χ′′/χ′ versus temperature, which may mean the existence of magnetic aftereffect, and furthermore, it has an Arrhenius as well as Vogel–Fulcher law type dependence. An observed nonthermal activation type relaxation mechanism at 12 K is attributed to possible quantum tunneling effect in Mn–Zn ferritenanoparticles.by Kinnari Parekh and R. V. Upadhya

Characterization of transformer oil based magnetic fluid

262-266In the present paper two different magnetic fluids synthesized earlier with transformer oil as carrier liquid are characterized. The magnetic properties of these fluids are studied using viscometry, magnetometer and Quincke’s technique. The properties of the magnetic fluid are compared with those of the pure transformer oil and the results are discussed

Dynamic Magnetic Properties of Monodispersed Fe3O4 Nanomagnetic particles

by Kinnari Parekh and R. V. Upadhya

Influence of temperature on thermal conductivity of CuO nanofluid

In the present article we report the synthesis of pure phase of CuO nanoparticles using Cu(NO:)z xH2O as precursor. The technique of synthesis is very fast, cheap and green materials technique. The CUO nanoparticles used in the experiment are rod-like, with a mean length of about 23-26 nm. They can be stably suspended in ethylene glycol for several months. Also stability of nanofluid prepared by such technique is better than that obtained by two step process. The effect of particle volume fraction and temperature on thermal conductivity of CuO-EG nanofluids developed using continuous chemical technique is studied. The thermal conductivity of the nanofluids was studied using the LAMBDA system based on the principle of instationary heat-wire instrument with a very small sensor. The output of the instrument is highly stable and reproducible. Experimental data indicates that the size, volume fraction and properties of nanoparticles (shape, nano layer thickness and material properties) influence the heat transfer characteristics of nanofluids. The experimental results show that the increase in therrnal conductivity with volume fraction is non-linear while that with temperature is linear. Further, the effect of temperature change on the thermal conductivity of nanofluids is greater than that of volume fraction change. For 1.78 percent of the volume fraction the rise in temperature from 25"C to 75oC enhances thermal conductivity by 10.5 percent to 20 percent. Therefore, when the copper oxide nanofluids are applied to the heat exchange device under medium and high temperature, an optimal radiation effect can be acquired.by Kinnari Parekh and H. S Le