Shreeja Pillai

Nanostructured La0.7Sr0.3MnO3 compounds for effective electromagnetic interference shielding in the X-band frequency range

We report a detailed study on the electromagnetic interference (EMI) shielding effectiveness (SE) properties in La0.7Sr0.3MnO3 (LSMO) nanomaterials. The samples were prepared by a solution chemistry (sol–gel) route at different sintering temperatures. The single-phase samples with grain sizes of 22 and 34 nm showed DC electrical conductivity variation from 0.65 to 13 S cm−1 at room temperature. The application of a high magnetic field resulted in higher conductivity values. The electrical conductivity variation with temperature could be fitted with a variable range hopping mechanism in a limited temperature range. The variation of frequency dependent electromagnetic parameters measured at room temperature within the X-band region is consistent with the electrical conductivity behavior. The complex permittivity and permeability parameters were determined in line with the Nicolson–Ross–Weir algorithm. The LSMO nanomaterial samples showed EMI shielding effectiveness values of up to 19 dB (96.3% attenuation) over the X-band frequency range, making them suitable for microwave radiation shielding in commercial and defense appliances.

Synthesis of single phase bismuth ferrite compound by reliable one-step method

We report the synthesis of polycrystalline BiFeO3 compound by solid state route and its structural and magnetic properties were investigated. The structure confirmation and phase purity of the samples were investigated by X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. No signature of thermodynamically probable impurity phases was observed in these samples. The Rietveld refined structural parameters of the XRD pattern revealed rhombohedral (R3c) structure. Scanning Electron Microscopy images show samples with larger grain size. The Raman active modes predicted by the group theory confirmed the rhombohedral symmetry. The study of the oxidation states of Bi, Fe and O through XPS analysis indicated that the sample quality is not deteriorated by vacancies or other defects formation. The absence of iron based impurity phases is confirmed by the antiferromagnetic nature of the sample obtained by magnetization measurements.

Bulk interface engineering for enhanced magnetization in multiferroic BiFeO3 compounds

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.

X-band frequency response and electromagnetic interference shielding in multiferroic BiFeO3 nanomaterials

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 BiFeO3 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 BiFeO3 nanomaterials. An auxiliary functionality of radiation shielding is revealed in the multiferroic BiFeO3 compound.

Kondo-like electronic transport and ferromagnetic cluster-glass behavior in La0.7Sr0.3MnO3 nanostructures

We have studied the electronic transport and magnetic properties of a nanocrystalline La0.7Sr0.3MnO3 system. The samples were prepared by sol–gel method and were sintered at different temperatures to achieve few nanometre grain sizes. The temperature dependent resistivity revealed Kondo like electronic transport at low temperature (T < 50 K) and variable range hopping in the paramagnetic insulating regime under zero and high magnetic field. The reduced grain size sample showed marginal increase in electrical resistivity. The temperature-field dependent ac-susceptibility measurement indicated the FM-cluster formation. A neck like magnetic hysteresis loop was observed due to the competition between ferromagnetic core and paramagnetic shell. The ferromagnetic clusters with paramagnetic interfaces impart glassy behavior.

Enhanced magnetization in morphologically and magnetically distinct BiFeO3 and La0.7Sr0.3MnO3 composites

Nanomaterials exhibit properties different from those of their bulk counterparts. The modified magnetic characteristics of manganite nanoparticles were exploited to improve magnetization in multiferroic BiFeO3 compound. We studied the composite of two morphologically and magnetically distinct compounds BiFeO3 (BFO) and La0.7Sr0.3MnO3 (LSMO). The microcrystalline BiFeO3 sample was prepared by solid state reaction method and the nanocrystalline La0.7Sr0.3MnO3 by sol-gel method. Composites with nominal compositions (1−x)BiFeO3–(x)La0.7Sr0.3MnO3 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 ...

Confirmation of enhanced magnetic moment in interface-engineered BiFeO3-LaMnO3 composites

We have confirmed the observation of a higher magnetic moment in the bulk composite of two distinct antiferromagnetic materials. The low temperature neutron diffraction technique was used for the structure and magnetic ordering study of polycrystalline samples with compositions (1-x)BiFeO3-xLaMnO3. The magnetic moment increased from 3.9 μB/f.u. for x = 0 to 4.3 μB/f.u. for x = 0.2 samples. The Fourier Transform Infra Red study indicated the structural invariance of the composite phases. The possibility of magnetic contribution from the multiple valencies of magnetic ions or oxygen vacancies was overruled on the basis of the X-ray Photoelectron Spectra analysis.

Modulation of magnetic interaction in Bismuth ferrite through strain and spin cycloid engineering

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.