Shreeja Pillai | Barkatullah University, Bhopal, India (original) (raw)

Papers by Shreeja Pillai

Journal of Applied Physics

BiFeO3–graphene oxide (BFO–GO) nanocomposites were synthesized through ultra-sonication under mil... more BiFeO3–graphene oxide (BFO–GO) nanocomposites were synthesized through ultra-sonication under mild heating, and their electromagnetic interference (EMI) shielding performance was investigated. The nanocomposites preserve the crystalline phase with R3c symmetry as analyzed by Rietveld refinement of x-ray diffraction data. The Raman spectroscopy and x-ray photoelectron spectroscopy studies confirm the formation of structured GO in nanocomposites samples. Magnetic hysteresis curves indicate unsaturated magnetic behavior. The interfacial polarization is dominating in BFO–GO composites as estimated from frequency dependent complex parameters determined in line with the Nicolson–Ross–Weir algorithm. The BFO–GO nanocomposites showed EMI shielding effectiveness of 18 dB (93% attenuation) over the measured frequency range. The oxide composite is a suitable EMI shielding material for techno-commercial applications.

$Research paper thumbnail of Structure and magnetization behavior of BiFeO 3 -LaMnO 3 composites studied using neutron diffraction$

Journal of Materials Science: Materials in Electronics, 2019

We present a detailed study on the structural, electronic, magnetic and dielectric properties of ... more We present a detailed study on the structural, electronic, magnetic and dielectric properties of La substituted multiferroic bismuth ferrite. Polycrystalline Bi 1 − x La x FeO 3 (0.1 ≤ x ≤ 0.3) samples were prepared by conventional solid state reaction method. The Rietveld refinement of x-ray diffraction data and Raman spectroscopy study showed clear indication of emergence of orthorhombic phase. Significant improvement in magnetic properties has been observed owing to the rhombohedral (R3c) to orthorhombic (Pnma) structural transition for 30 mol% La substituted sample. The x-ray photoelectron spectroscopy study confirmed the absence of mixed valency or detectable vacancies. Therefore, the increase in magnetization is the attribute of structural variance. The dielectric behavior showed initial increase in permittivity with La substitution but further decrease with structural change.

SPIE Proceedings, 2016

Bismuth ferrite, a widely studied room temperature multiferroic, provides new horizons of multifu... more Bismuth ferrite, a widely studied room temperature multiferroic, provides new horizons of multifunctional behavior in phase transited bulk and thin film forms. Bismuth ferrite thin films were deposited on lattice mismatched LaAlO3 substrate using pulsed laser deposition technique. X-ray diffraction confirmed nearly tetragonal (T-type) phase of thin film involving role of substrate induced strain. The film thickness of 56 nm was determined by X-ray reflectivity measurement. The perfect coherence and epitaxial nature of T- type film was observed through reciprocal space mapping. The room temperature Raman measurement of T-type bismuth ferrite thin film also verified phase transition with appearance of only few modes. In parallel, concomitant La and Al substituted Bi1-xLaxFe0.95Al0.05O3 (x = 0.1, 0.2, 0.3) bulk samples were synthesized using solid state reaction method. A structural phase transition into orthorhombic (Pnma) phase at x = 0.3 was observed. The structural distortion at x = 0.1, 0.2 and phase transition at x = 0.3 substituted samples were also confirmed by changes in Raman active modes. The remnant magnetization moment of 0.199 emu/gm and 0.28 emu/gm were observed for x = 0.2 and 0.3 bulk sample respectively. The T-type bismuth ferrite thin film also showed high remnant magnetization of around 20emu/cc. The parallelism in magnetic behavior between T-type thin film and concomitant La and Al substituted bulk samples is indication of modulation, frustration and break in continuity of spiral spin cycloid.

Journal of Materials Science: Materials in Electronics, 2016

We report synthesis of double perovskite La2CoMnO6 compound by a simple solid state reaction meth... more We report synthesis of double perovskite La2CoMnO6 compound by a simple solid state reaction method. The samples sintered at different temperatures showed single phase nature with monoclinic P21/n space group. The phase purity was confirmed through the presence of characteristic Raman scattering modes. The samples exhibited semiconducting behavior without any anomaly in the temperature range 125 K ≤ T ≤ 300 K. The maximum magnetoresistance value at low temperature was around 40 %. The electric and magneto-transport behaviors were governed by variable range hopping mechanism. A single paramagnetic to ferromagnetic transition and well saturated hysteresis loops, indicative of ordered phase were observed in these samples.

Journal of Applied Physics, 2016

Articles you may be interested in Intrinsic defect-mediated conduction and resistive switching in... more Articles you may be interested in Intrinsic defect-mediated conduction and resistive switching in multiferroic BiFeO3 thin films epitaxially grown on SrRuO3 bottom electrodes

Applied Physics A, 2016

Structural, optical and polarization properties were investigated in different batches of ZnO syn... more Structural, optical and polarization properties were investigated in different batches of ZnO synthesized by sol–gel method at varying sintering temperature. The structural visualization and charge scattering density analysis on the basis of X-ray diffraction data indicate polarized nature of sample. The structure- and polarization-related parameters were determined from Raman and Fourier transformed infrared spectroscopy data. Urbach energies and band gap were calculated using UV–visible spectroscopy. We observed increase in polarization, decrease in optical activity and band gap with increasing grain size without any increase in defects. Distortion in ZnO tetrahedra resulted in nonlinear optical behaviour above band edges. The results show direct correlation between grain size, band gap, optical behaviour and polarization. Low band gap and high polarization in ZnO can be employed for the production of opto-electronic devices.

ABSTRACT The rare earth manganite with composition La0.7Sr0.3MnO3 is known as large bandwidth com... more ABSTRACT The rare earth manganite with composition La0.7Sr0.3MnO3 is known as large bandwidth compound which can impart almost 100% spin polarization. It has high paramagnetic- ferromagnetic transition temperature due to large bandwidth of single electron hopping. However, the well established phase diagram does not show signature of metal-insulator transition for this particular composition. This material also exhibits high magnetoresistance (MR) value at lower temperature with high applied magnetic field. From application point of view, it is important to achieve significant MR value with low magnetic field

Journal of Materials Chemistry C, 2015

EMI shielding effectiveness values of up to 19 dB are observed in LSMO nanomaterials.

Journal of Materials Science: Materials in Electronics, 2014

ABSTRACT We have investigated electrical and magnetotransport properties of La0.7Sr0.3MnO3 sample... more ABSTRACT We have investigated electrical and magnetotransport properties of La0.7Sr0.3MnO3 samples with grain size in micro to nanometric regime. The structural parameters obtained by Rietveld refinement of X-ray diffraction data revealed perovskite structure with orthorhombic (Pnma) and rhombohedral (R3C) symmetry for nano and bulk samples respectively. The average particle size was 22 nm and 2 mu m for the two representative samples. A metal-insulator transition and substantial increase in electrical resistivity was observed in nanomaterials. An enhanced magnetoresistance observed in nanomaterials samples, makes them more promising for advanced device applications. The magnetization study showed signature of ferromagnetic cluster behavior and higher temperature coefficient of magnetization in nanoparticle samples.

Journal of Materials Science: Materials in Electronics, 2013

Applied Physics Letters, 2013

We investigated composites of two antiferromagnetic perovskite oxides BiFeO3 and LaMnO3 to study ... more We investigated composites of two antiferromagnetic perovskite oxides BiFeO3 and LaMnO3 to study change in bulk magnetic behavior. Composites with nominal compositions (1−x)BiFeO3-xLaMnO3 (x = 0, 5, 10, 20 wt. %) were synthesized by solid state reaction route. The structural analysis performed using X-ray diffraction and Raman spectroscopy indicated presence of phase separated compounds. Significant enhancement in magnetic moment is observed in composite samples, which was attributed to the uncompensated spins at the interface of two distinct antiferromagnetic phases.

Journal of Nanoscience and Nanotechnology, 2013

Applied Physics Letters, 2016

The presence of electric dipoles, magnetic dipoles and mobile charges is a prerequisite for elect... more The presence of electric dipoles, magnetic dipoles and mobile charges is a prerequisite for electromagnetic interference (EMI) shielding materials. Here, we demonstrate that multiferroic compound with incipient ensemble of electric and magnetic dipoles can perform as an EMI shielding material. We synthesized single phase BiFeO 3 nanomaterial and studied complex electromagnetic properties in an X-band frequency region. A shielding effectiveness up to 11 dB with a major contribution from absorption was observed in the BiFeO 3 nanomaterials. An auxiliary functionality of radiation shielding is revealed in the multiferroic BiFeO 3 compound. Published by AIP Publishing.

Journal of Applied Physics, 2017

Nanomaterials exhibit properties different from those of their bulk counterparts. The modified ma... more Nanomaterials exhibit properties different from those of their bulk counterparts. The modified magnetic characteristics of manganite nanoparticles were exploited to improve magnetization in multiferroic BiFeO 3 compound. We studied the composite of two morphologically and magnetically distinct compounds BiFeO 3 (BFO) and La 0.7 Sr 0.3 MnO 3 (LSMO). The microcrystalline BiFeO 3 sample was prepared by solid state reaction method and the nanocrystalline La 0.7 Sr 0.3 MnO 3 by solgel method. Composites with nominal compositions (1Àx)BiFeO 3-(x)La 0.7 Sr 0.3 MnO 3 were prepared by modified solid state reaction method. The phase purity and crystal structures were checked by using X-ray diffraction. The formation of composites with phase separated BFO and LSMO was confirmed using Raman and Fourier Transform Infrared spectroscopy studies. The composite samples showed relatively high value of magnetization with finite coercivity. This improvement in magnetic behavior is ascribed to the coexistence of multiple magnetic orderings in composite samples. We scrutinized the possibility of oxygen vacancy or Fe mixed valency formation in the samples using X-ray photoelectron spectroscopy technique. Published by AIP Publishing.

RSC Advances

We have studied the electronic transport and magnetic properties of a nanocrystalline La0.7Sr0.3M... more We have studied the electronic transport and magnetic properties of a nanocrystalline La0.7Sr0.3MnO3 system. We observed low temperature Kondo effect with magnetic cluster behavior.

Low-loss NiCuZn ferrite with matching permeability and permittivity by two-step sintering process... more Low-loss NiCuZn ferrite with matching permeability and permittivity by two-step sintering process J. Appl. Phys. 113, 17B301 Real-time observation of electrical vortex core switching Appl. Phys. Lett. 102, 072405 Transport of perpendicular spin in a semiconductor channel via a fully electrical method Appl. Phys. Lett. 102, 062412 (2013) Oxygen stoichiometry and magnetic properties of LuFe2O4+δ J. Appl. Phys. 113, 063909 (2013) Correlation between structural parameters and the magnetocaloric effect in epitaxial La0.8Ca0.2MnO3/LaAlO3 thin film