Manju Lata Rao

Microwave synthesis and characterization of doped ZnS based phosphor materials

We report here the synthesis and characterization of a host of ZnS-based phosphor materials employing microwave radiation. Activator ions such as Cu, Ag and Mn have been successfully doped. Microwave method enables higher doping percentage of Cu, upto 10% in ZnS. These materials have been characterized using XRD, SEM, EPMA, and the emission spectral studies. The effect of higher doping concentrations and narrow particle size distribution of the microwave-prepared samples is clearly reflected in the emission spectra.

Microwave synthesis of magnetoresistive La0.7Ba0.3MnO3 using inorganic precursors

We report here the use of inorganic precursors as good microwave absorbers, by virtue of its polarity and high dielectric constant, to synthesize high temperature stable rare earth manganite, La0.7Ba0.3MnO3. Compared to other wet chemical methods, the oxides prepared by microwave assisted route give fine particle oxides (<30 nm) with effective BET surface area of ∼25 m2/g. Two factors contribute to the rapid synthesis of these high temperature phases. Firstly, the dielectric constant of the precursors employed increases the microwave power loss in the material and this leads to a local heating effect. Secondly decomposition of these precursors, lead to formation of finely divided oxides often accompanied by an exothermic reaction which provides the needed energy to effect the formation of the product. This method offers a new approach to employ inorganic precursors as starting materials to realize fast and effective reaction in microwave assisted material synthesis.

Long range ferromagnetic ordering in pulsed laser deposited La0.7Ca0.3Mn1−xRuxO3 thin films

We demonstrate the existence of the metal to insulator transition (TMIT) up to 30% of Ru substitution at the Mn site, while the ferromagnetic transition (TC) is sustained even beyond 30% Ru substitution in the pulsed laser deposited La0.7Ca0.3Mn1−xRuxO3 thin films. The presence of Ru(IV) and (V) states complementing the t2g and eg orbital parentage of Mn(III) and Mn(IV) brings about prolonged double exchange mediated magnetic and electronic interactions, as confirmed by the X-ray absorption spectra and a negative magneto resistance ratio (MR) up to 11% at TMIT even for 30% Ru substitution.

One-pot sonochemical synthesis of Fe1-xCuxCr2S4 chalcospinels

We present a simple and convenient one step route to prepare a series of chalcospinels Fe1−xCuxCr2S4 employing high frequency sound waves. The magnetic and electronic transport properties of the as-prepared spinels were studied, and this simple, easy, and efficient synthetic route may further encourage wider application of Cu-doped Fe chalcogenides in solid state magnetoelectronic devices. Furthermore, the adopted synthetic route highlights a one-pot synthesis employing organometallic precursors such as metal carbonyls, ethylenedimine, and elemental sulfur. The ease of synthesizing such complex spinel structures of Fe1−xCuxCr2S4 chalcogenides with x=0.3, 0.4, and 0.6 has been highlighted in this work. The rapid cavitational collapse results in sulfur deficiency in the system, which drastically alters the conduction behavior. All the compositions studied show a negative magnetoresistance response except for x=0.3 which exhibit an unusual positive magnetoresistance effect. Such an effect has been attributed...

Influence of hole carrier density and sintering temperature on the electronic properties of magnetoresistive La 0.7 Pb 0.3 Mn 1⊟ x Ru x O 3 (0.0 ≤ x ≤x 0.4)

A novel magnetic pair-making interaction between Mn and Ru shows a strong correlation between the magnetic ordering and electronic transport, which was well exemplified in the investigation of bulk polycrystalline samplesof La 0 . 7 Pb 0 . 3 Mn 1 - x Ru x O 3 and La 0 . 6 Pb 0 . 4 Mn 1 - x Ru x O 3 , where 0.0 ≤ x ≤ 0.4. The metal-insulator transition (T p ) complementing the Curie temperature (T c ) was observed up to 30% of Ru in La 0 . 7 Pb 0 . 3 Mn 1 - x Ru x O 3 , and extended up to 40% of Ru in La 0 . 6 Pb 0 . 4 Mn 1 - x Ru x O 3 , showing a unique double-exchange ferromagnetic exchange interaction between Mn and Ru ions. An upturn in resistance due to charge carrier localization at low temperatures (T< 0.5 T c ) for more than 20% Ru doping was due to a dominant hole carrier density contribution rather than to grain boundary effects as inferred from the scanning electron microscopy and energy dispersive x-ray studies of the samples sintered at 1200 and 1400 °C. The charge localization effect of the e g electrons was removed by tuning the hole carrier density as demonstrated in the La 0 . 6 Pb 0 . 4 Mn 1 - x Ru x O 3 samples. Long range correlations between magnetism and transport in this series was attributed to the presence of mixed valence Ru(IV/V) and Mn(III)/(IV) pair, which shows a unique double exchange mediated interaction.