Deba Prasad Paul

Effect of Grain Size on Structural and Magnetic Properties of CuFe

CuFe2O4 nanograins have been prepared by the chemical co-precipitation technique and calcined in the temperature range of 200-1200°C for 3 h. A wide range of grain sizes has been observed in this sintering temperature range, which has been determined to be 4 to 56 nm. Formation of ferrite has also been confirmed by FTIR measurement through the presence of wide band near 600 and 430 cm-1 for the samples in the as-dried condition. Systematic variation of wave number has been observed with the variation of the calcination temperature. B-H loops exhibit transition from superparamagnetic to ferrimagnetic state above the calcination temperature of 900°C. Coercivity of the samples at lower calcination temperature of 900°C reduces significantly and tends towards zero coercivity, which is suggestive of superparamagnetic transition for the samples sintered below this temperature. Frequency spectrum of the real and imaginary part of complex initial permeability have been measured for the samples calcined at different temperature, which shows wide range of frequency stability. Curie temperature, Tc has been measured from temperature dependence initial permeability at a fixed frequency of 100 kHz. Although there is small variation of Tc with sintering temperature, the reduction of permeability with temperature drastically reduce for lower sintering temperature, which is in conformity with the change of B-H loops with the variation of sintering temperatures.

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The magnetic properties of nanocrystalline Fe74Cu0.8Nb2.7Si15.5B7 alloy, which were rapidly solidified and then annealed at various temperatures between 475 and 650°C for different holding time, have been studied. Grain size, silicon content and the lattice parameter of α-Fe(Si) nanograins at the annealing temperatures were determined. Curie temperature of the amorphous phase was determined from the temperature dependence of permeability. For higher annealing temperatures and times, some Si diffused out of the α-Fe(Si) phase and formed an ordered DO3 phase of Fe3Si. This changed the overall magnetostriction and average anisotropy of the matrix, which deteriorated the magnetic softness of the material at higher annealing temperatures. Ultra-soft magnetic properties were achieved by averaging the random anisotropy via exchange interaction. Hysteresis loops for samples in as-cast and annealed conditions have also been studied.

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Abstract The present work investigates the texturing and superconducting properties of Sm substituted Bi 2 Sr 2 CaCu 2 O 8+δ (Bi-2212) crystals grown by the floating zone technique. The texturing nature of Bi-2212 was quantified by X-ray diffraction and by scanning electron microscopic studies. The texturing nature varies with respect to the ‘Sm’ concentration. Superconductivity studies were carried out by the resistivity technique and the transition temperature increases from 78K to 85K (for x=0.2) and decreases for higher concentration. The c-lattice parameter decreases with Sm substitution.

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Abstract Theoretical investigations have been made to calculate the nucleation thermodynamical parameters like interfacial energy between the solid Nd123 and its flux BaO–CuO, metastable zone-width, volume free energy, critical energy barrier for nucleation and radius of critical nucleus from the knowledge of solubility data and by applying the classical nucleation theory. Results are discussed to understand the growth kinetics of Nd123 crystals from a high temperature solution.

Nanograins Synthesized by Chemical Co-Precipitation

Abstract In the present work, Cu1-xMgxFe2O4 (x = 0.2, 0.4, 0.6, 0.8 and 1.0) ferrites have been synthesized via a conventional solid-state reaction method. Thermal analysis and the estimation of total weight loss of the samples were performed by differential thermal analysis and thermogravimetric analysis measurements. The thermal variation of initial permeability exhibits unusual dependence with the manifestation of a broad hump followed by a Hopkinson peak attributed to the structural transformation and minimization of magneto-crystalline anisotropy energy, respectively. A decrease in resistivity is observed with increase in temperature and corresponding activation energies for conduction have been calculated. Possible explanations for the observed physical, thermal, magnetic and transport properties with temperature of the samples are discussed in the present paper.

Detailed study of ultra-soft magnetic properties of Fe74Cu0.8Nb2.7Si15.5B7

A series of Li0.5−x/2CdxBi0.02Fe2.48−x/2O4 ferrites for x = 0.0 to 0.7, were prepared by conventional double sintering ceramic technique. The lattice parameter is found to increase linearly with Cd content. SEM micrographs reveal that an increase of grain size is observed up to x = 0.4 with increasing Cd content and then the grain size decreases slowly with further increase of Cd content. Similar trend is observed in the variation of saturation magnetization Ms with Cd content. This is explained on the basis of Neel’s and Yafet‐Kittle (Y‐K) model. The Curie temperature also decreases linearly with Cd content and is due to the decrease in the strength of the A‐B exchange interaction. DC resistivity and AC resistivity is found to decrease with increasing Cd content and frequency respectively.