Sunita Keshri

Enhanced CMR properties of La0.67Ca0.33MnO3 sintered at different temperatures

This article reports the study of the magneto-transport properties of Lanthanum-based colossal magnetoresistive sample, , as a function of temperature. The samples were prepared by the solid state route by sintering at three different temperatures 1100°C, 1250°C and 1350°C; with a view to understand the influence of varying crystallite size on various physical properties. It has been observed that the change in the grain size with the sintering temperature alters the contributions of intrinsic and extrinsic resistances which results in some major effects on the magneto-transport behaviours. The occurrence of intrinsic and extrinsic transitions can be explained well by the consideration of the random network of resistances with two types of resistivities – one more resistive than the other; using time dependent and independent metallic volume fractions, respectively.

Synthesis and characterization of LSMO manganite-based biocomposite

In this paper we study the structural, morphological and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite nanoparticles (NPs) and its biocomposite, obtained by mixing NPs of hydroxyapatite (HA). From the studies of X-ray diffraction and Fourier transmission of infrared spectroscopy it is evident that in the biocomposite sample both the individual phases are distinguishable from each other. The measurements of direct current (DC) magnetization and hysteresis loops reveal that the basic magnetic behaviour of LSMO–HA is similar to that of LSMO; however, the admixture of HA makes the sample magnetically softer. From the investigation of transmission electron microscopy it is observed that such a biocomposite is composed of the NPs of LSMO surrounded by HA particles, which can be found suitable for biomedical applications.

Structural and magneto-transport properties of LCMO–STO composites

A manganite matrix-based composite series, (1 − x)La0.67Ca0.33MnO3(LCMO) − (x)SrTiO3 (STO), has been prepared by the solid state route. Influence of STO phase on structural and magneto-transport properties of LCMO phase has been investigated. By X-ray diffraction, scanning electron microscopy, and Fourier transform of infrared spectroscopy, we find that there is no interdiffusion between the LCMO and STO phases. Measurements of resistivity on these samples reveal that the parent sample shows a distinct metal–insulator (M–I) transition of intrinsic type at a temperature close to the Curie temperature, whereas composite samples show two possible transitions, intrinsic as well as extrinsic. The series exhibits a conduction threshold at x = x m ∼ 20%, up to which extrinsic M–I transition temperature decreases along with an increase in extrinsic magnetoresistance; whereas, above x m these trends of variation are reversed.

Influence of Fe doping on electrical properties of LCMO

The polycrystalline samples La0.67Ca0.33Mn(1−x)Fe x O3 (x = 0.00, 0.01, 0.03, and 0.1) have been grown in single phase by solid state route. The analysis of the reaction has been done by thermogravimetry and differential thermal analysis measurements. DC electrical resistivity measurements have been carried out down to 15 K. The samples with x = 0.00, 0.01, and 0.03 exhibit metal–insulator (MI) transition at temperatures 221.5 K, 217 K, and 215 K respectively, whereas the sample with x = 0.1 is insulating in nature for entire temperature range. Interestingly, the electric transport properties of these samples are not consistent with their magnetic phase transitions and the samples show MI transition at a temperature, T MI, which is significantly lower than the paramagnetic to ferromagnetic transition temperature (T c). The resistivity data below T MI has been analyzed using the empirical relation ρ = ρ0 + ρ1 T n and the data above this temperature has been analyzed using two existing models, Motts variable range hopping model and spin polaronic conduction model.

Electronic transport in LCMO/BTO composites

A series of (1 − x)La0.67Ca0.33MnO3/(x)BaTiO3 composites has been synthesized by the solid state route. Microstructural and transport studies on these samples show a complete immiscibility between metallic ferromagnet, La0.67Ca0.33MnO3 (LCMO) and insulating ferroelectric, BaTiO3 (BTO). Temperature dependent electrical transport studies show evidence of both intrinsic and extrinsic colossal magnetoresistance (CMR) effects. Inclusion of BTO in LCMO phase results in high resistive samples with a metal-insulator transition at temperature Tp 1 originating from intrinsic effect and another dominant metal-insulator transition at temperature Tp 2 caused because of extrinsic effect. Tp 2 decreases up to a certain percentage of BTO content above which this trend of variation is reversed.

Effect of BTO addition on the structural and magnetoresistive properties of LSMO

In the present paper we report the structural and magnetoresistive properties of the composite series with ; both the phases have been prepared using the chemical route method. With the BTO addition, the metal–insulator transition temperature () decreases till some optimum value of , after which it increases again. The inclusion of BTO causes an enhancement in magnetoresistance (MR) over a wide temperature range and it is maximum for the sample with . An increase in MR for the composite samples can be explained on the basis of the spin-dependent scattering and tunnelling of conducting electrons.

Effect of γ-irradiation on the transport and structural properties of polycrystalline Bi1.2 Pb0.33 Sr1.54 Ca2.06 Cu3 O10+δ superconductor

The effect of γ-irradiation on the transport and structural properties of polycrystalline Bi1.2 Pb0.33 Sr1.54 Ca2.06 Cu3 O10+δ superconductor, synthesized by nitrate route is studied. The sample has been irradiated by γ-ray upto a dose 400 MR using a 60Co isotope source of 2 kCi strength with a dose-rate of 6.26 Gy/min. Its X-ray diffraction pattern, resistivity–temperature behaviour as well as elemental and morphological analyses using scanning electron microscope have been examined before and after the irradiation. It is observed that the normal state resistivity increases as the dose is increased. The transition width of the sample is found to get broadened with the increasing dose. Using the theories of Aslamazov–Larkin and Maki–Thompson, we present an analysis of the excess conductivity of our sample and the effect of γ-irradiation on it. It is found that the coherence length of the sample gets increased with the increase of the irradiation dose.

Temperature stable ZnTa2O6 dielectric ceramic with 2% W6+ ion substitution in Ta5+ site

ABSTRACT This paper reports the study of structural, morphological and microwave dielectric properties of Zn(Ta1-xWx)2O6 (x = 0–0.05) ceramics, sintered at 1225–1325 C. The X-ray diffraction data show that the samples have tri-- orthorhombic structure. The microwave dielectric properties of the grown samples were thoroughly studied using Hakki–Coleman dielectric resonator method. It is observed that the dielectric properties of these samples are strongly dependent on their compositions and microstructures. The Zn(Ta0.98W0.02)2O6 sample, possessing an excellent combination of dielectric properties with relative permittivity of 21.1, quality factor of 38,500 GHz (measured at 8.57 GHz) and zero temperature coefficient of resonant frequency, is investigated as a suitable material for microwave applications.

Antibiotic loading and release studies of LSMO nanoparticles embedded in an acrylic polymer

ABSTRACT In this paper, we present the drug loading and release works of (LSMO) manganite nanoparticles (NPs). The LSMO NPs, grown using the sol–gel method, were embedded in an acrylic interpenetrating polymer network to make the sample applicable for biomedical purposes. The results of scanning electron microscopy showed that these NPs were well dispersed in the polymer. The grain size of these NPs lies in the range of 25–45 nm, as confirmed by transmission electron microscopy. The measurements of DC magnetization and hysteresis loops reveal that the basic magnetic behaviour of the LSMO NPs remained almost unaltered even after embedding in polymer, but with lower saturation value of magnetization. The drug loading and release studies of the grown sample were carried out using an antibiotic, ciprofloxacin. The minimum inhibitory effect of the sample loaded with this drug has exhibited high activity against different strains of bacteria, comparable to the pure ciprofloxacin.

Impact of N5+ ion implantation on optical and electrical properties of polycrystalline ZnO film

A combined study on structural, vibrational, optical and carrier conductivity behaviours has been carried out on ZnO films implanted with 45 keV N5+ ions with a fluence of 1 × 1015−1 × 1017 cm−2. The paper provides an interesting result that the sample implanted with the highest fluence of 1 × 1017 cm−2 shows p-type conductivity at room temperature with a reasonably high carrier concentration of . All implanted samples show negative magnetoresistance and its value increases with the increase in the magnetic field as well as fluence. The maximum negative MR value at 5 K, obtained by the application of 8 T magnetic field, has been found to be −11.8% for the film with the highest fluence of 1 × 1017 cm−2.