• R V Upadhyay

      Articles written in Bulletin of Materials Science

    • Magnetocaloric effect in temperature-sensitive magnetic fluids

      Kinnari Parekh R V Upadhyay R V Mehta

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      The magnetocaloric properties of three different temperature-sensitive magnetic fluids were studied. The pyromagnetic coefficient for all the materials were obtained and it was found that this property depends on physical and magnetic properties like size, magnetization and Curie temperature. A theoretical model was developed to explain the behaviour of change in entropy with temperature.

    • Magnetically textured ferrofluid in a non-magnetic matrix: Magnetic properties

      Mrudul Gadhvi R V Upadhyay Kinnari Parekh R V Mehta

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      Texturing of two different magnetic fluids were carried out in paraffin wax under the influence of an external magnetic field. The textured samples were characterized using magnetization measurement and a.c. susceptibility techniques. The results are discussed in the light of ratio of anisotropic energy to magnetic and thermal energies.

    • Bulk magnetic properties of CdFe2O4 in nano-regime

      Rucha Desai R V Mehta R V Upadhyay Amita Gupta A Praneet K V Rao

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      Cadmium ferrite particles have been synthesized using co-precipitation technique followed by a low temperature (600°C) annealing in a time scale much shorter than reported in literature. Incorporation of sodium chloride during annealing helps to form a single phase spinel structure with a final particle size of around 50 nm. Even at such a short length scale we observe the overall magnetic properties to be similar to those of the bulk. The observed magnetic properties can be explained on the basis of an anti-ferromagnetic core with a shell containing ‘ferromagnetic-like’, but canted spin structure.

    • Low temperature synthesis of nanosized Mn1–𝑥Zn𝑥Fe2O4 ferrites and their characterizations

      Rajesh Iyer Rucha Desai R V Upadhyay

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      Nanosized Mn1–𝑥Zn𝑥Fe2O4 (𝑥 = 0, 0.1, 0.3, 0.5, 0.6, 0.7, 0.9) mixed ferrite samples of particle size < 12 nm were prepared using the co-precipitation technique by doping the Zn2+ ion impurities. Autoclave was employed to maintain constant temperature of 80°C and a constant pressure. The X-ray analysis and the IR spectrum analysis were carried out to confirm the spinel phase formation as well as to ascertain the cation distribution in the ferrite samples. This clearly points to the fact that the Zn2+ ion’s presence is not restricted to A-site alone for some of the Mn–Zn ferrite series. The real part of a.c. susceptibility measurements clearly indicated the superparamagnetic behaviour of the ferrite samples. There is a systematic decrease in the particle size, Curie temperature and magnetization with the increase in the Zn2+ ion doping, measured using magneto thermal gravimetric analysis (MTGA) and vibrating sample magnetometer (VSM), respectively. The lattice constant is found to be constantly decreasing till 𝑥 = 0.6 and beyond this an unusual slight increase in the lattice constant is found.

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      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
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