Papers by Basavaraj Angadi
Materials Today: Proceedings, 2016
Journal of Superconductivity and Novel Magnetism, 2016
Journal of Magnetism and Magnetic Materials, 2016
Advanced Science Letters, 2016
We report on the single phase synthesis and room temperature structural characterization of PbFe0... more We report on the single phase synthesis and room temperature structural characterization of PbFe0.67W0.33O3 (PFW) multiferroic. The PFW was synthesized by low temperature sintering, Columbite method. Analysis of powder XRD pattern exhibits single phase formation of PFW with no traces of pyrochlore phase. Detailed analysis of room temperature neutron diffraction (ND) reveals cubic phase at room temperature, space group Pm-3m. The ND pattern clearly reveals magnetic Bragg peak at 2theeta = 18.51 (Q = 1.36{\AA}-1). The refinement of magnetic structure reveals G-type antiferromagnetic structure in PFW at room temperature. The dielectric constant and loss tangent decreases with increasing frequency. The room temperature P-E measurements shows a non-linear slim hysteresis, typical nature of relaxor multiferroics, with saturation and remnant polarizations of Ps = 1.50 microC/cm2 and Pr = 0.40 microC/cm2, respectively.
Journal of Materials Science, 2015
Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb... more Neutron diffraction (ND) studies were carried out on polycrystalline single-phase multiferroic Pb(Fe 0.5-Nb 0.5 )O 3 (PFN) in the temperature range of 290-2 K to understand the structural and magnetic properties as a function of temperature. ND data were refined using the Rietveld refinement method for both crystallographic and magnetic structures. The structure at room temperature was found to be monoclinic, in Cm space group. No structural transition was observed till 2 K. At low temperatures (i.e., from T \ T N ; T N = 155 K), an additional peak appears at scattering vector, Q = 1.35 Å -1 , indicating the onset of antiferromagnetic ordering. The magnetic structure was found to be commensurate with the crystallographic structure and could be refined using the propagation vector, k = [0.125, 0.5, and 0.5]. Magnetization, ferroelectric P-E loops, and dielectric measurements on PFN reveal a strong anomaly at the antiferromagnetic transition temperature (T N ) indicating the magneto-electric coupling. The refined temperature-dependent structural parameters such as unit cell volume and monoclinic distortion angle (b) reveal pronounced anomalies at the magnetic ordering temperature (T N ), which indicates strong spin-lattice coupling. An anomaly in lattice volume was observed with a small negative thermal expansion below and a large thermal expansion above the T N , respectively. It shows the occurrence of isostructural phase transition accompanying the magnetic ordering below T N *155 K, leading to significant change in ionic polarization, octahedral tilt angle, and lattice strain around T N . We have used refined atomic positional coordinates from the nuclear and magnetic structures, to obtain ionic polarization. These detailed studies confirm the magneto-electric and spin-lattice coupling in PFN across T N .
Ceramics International, 2015
We report the origin of room temperature weak ferromagnetic behavior of polycrystalline Pb(Fe 2/3... more We report the origin of room temperature weak ferromagnetic behavior of polycrystalline Pb(Fe 2/3 W 1/3 )O 3 (PFW) powder. The structure and magnetic properties of the ceramic powder prepared by a Columbite method were characterized by X-ray and neutron diffraction, Mössbauer spectroscopy and magnetization measurements. Rietveld analysis of diffraction data confirm the formation of single phase PFW, without traces of any parasitic pyrochlore phase. PFW was found to crystallize in the cubic structure at room temperature. The Rietveld refinement of neutron diffraction data measured at room temperature confirmed the G-type antiferromagnetic structure of PFW in our sample. However, along with the antiferromagnetic (AFM) ordering of the Fe spins, we have observed the existence of weak ferromagnetism at room temperature through: (i) a clear opening of hysteresis (M-H) loop, (ii) bifurcation of the field cooled and zero-field cooled susceptibility; supported by Mössbauer spectroscopy results. The P-E loop measurements showed a non-linear slim hysteresis loop at room temperature due to the electronic conduction through the local inhomogeneities in the PFW crystallites and the inter-particle regions. By corroborating all the magnetic measurements, especially the spin glass nature of the sample, with the conduction behavior of the sample, we report here that the observed ferromagnetism originates at these local inhomogeneous regions in the sample, where the Fe-spins are not perfectly aligned antiferromagnetically due to the compositional disordering.
Journal of Superconductivity and Novel Magnetism, 2015
We report the origin of room temperature (RT) ferromagnetic and ferroelectric properties of Pb(Fe... more We report the origin of room temperature (RT) ferromagnetic and ferroelectric properties of Pb(Fe 1/2 Nb 1/2 )O 3 (PFN) ceramic sample prepared by modified solid-state reaction synthesis by a single-step method, based on X-ray diffraction (XRD), neutron diffraction (ND), Mössbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy results. Formation of singlephase monoclinic PFN ceramic with Cm space group was confirmed by XRD and ND at RT. The morphology studied by scanning electron microscopy (SEM) confirmed uniform microstructure of the sample with average grain size of ∼ 2 μm. The ND, Mössbauer spectroscopy, M-H loop and EPR studies were carried out to confirm the existence of weak ferromagnetism at RT. A clear opening of hysteresis (M-H ) loop is evidenced as the existence of weak ferromagnetism at RT. EPR spectrum clearly shows the ferromagnetism through a good resonance signal. The symmetric EPR line shape with g = 1.9895 observed in PFN sample was identified to be due to Fe 3+ ions. Mössbauer spectroscopy at RT shows superparamagnetic behaviour with presence of Fe in 3+ valence state. Ferroelectric P -E loops on PFN at RT confirm the existing ferroelectric ordering. Our observation is in agreement with literature, and it supports that the origin of ferromagnetism and ferroelectricity is isolated, i.e. from different regions in the sample. Our results do not support the multiferroic nature of PFN at RT.
Optical Materials Express, 2014
ABSTRACT The dielectric/Ag structures were fabricated on glass substrates using various metal oxi... more ABSTRACT The dielectric/Ag structures were fabricated on glass substrates using various metal oxides as dielectrics and their optical properties were studied through transmittance and ellipsometry measurements. The structures with 10 nm Ag film deposited on various metal oxides (Al2O3, ZrO2, SrTiO3, TiO2, CaCu3Ti4O12, WO3 and HfO2) of 30 nm showed enhancement in transmittance compared to bare Ag film in the visible region. This enhancement in transmittance was explained through suppression of surface plasmon coupling at the dielectric/Ag interface. The surface plasmon wave-vector (kSP) was calculated using the measured dielectric constants for the dielectric and Ag through ellipsometry and employed to analyze the transmittance data. The kSP/k0 and δSP values were estimated and used to interpret the enhanced visible transmittance for different dielectric/Ag structures.
Journal of Electron Spectroscopy and Related Phenomena, 2014
ABSTRACT Pure and Co substituted ZnO nano crystalline particles were prepared by solution combust... more ABSTRACT Pure and Co substituted ZnO nano crystalline particles were prepared by solution combustion technique using L-Valine as a fuel. As synthesized powder samples were characterized by X-ray Diffractometer and SQUID magnetometer to confirm the formation of single phase wurtzite structure and to study the bulk magnetic response of the sample, respectively. Magnetic studies show that Co doped ZnO nanoparticles exhibit ferromagnetism (FM) at room temperature (RT). Furthermore, the electronic structure and element specific magnetic properties were investigated by near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) measurements, respectively. The effect of Co substitution on the spectral features of Co-ZnO at O K edge, Co L3,2 edge, Zn L3,2 edge have been investigated. The spectral features of NEXAFS at Co L3,2 edge is entirely different from the spectral features of metallic clusters and other impurity phases, which rules out the presence of impurity phases. The valence state of ‘Co’ ion is found to be in +2 state. The FM nature of the sample was confirmed through XMCD spectra, which is due to the incorporation of divalent ‘Co’ ions. Hence the presented results confirm the substitution of ‘Co’ ions at ‘Zn’ site in the host lattice, which is responsible for the RTFM.
Journal of the Korean Physical Society, 2014
ABSTRACT
Advanced Energy Materials, 2015
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Papers by Basavaraj Angadi