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    Correlation between structural, magnetic and ferroelectric properties of Fe-doped (Ba-Ca)TiO3 lead-free piezoelectric
    (Elsevier Ltd, 2017) Keswani, B.C.; Devan, R.S.; Kambale, R.C.; James, A.R.; Manandhar, S.; Kolekar, Y.D.; Ramana, C.V.
    The effect of iron (Fe) doping modification on the structure and properties of Ba0.92Ca0.08TiO3 (BCT8) lead-free ferroelectrics is investigated in detail. Intrinsic BaTiO3 (BT) and Ba0.92Ca0.08TiO3 (BCT8) lead-free polycrystalline ceramics were synthesized by conventional solid-state chemical reaction method. The crystal structure, morphology, chemical composition and valence state, magnetic and ferroelectric properties of BCT8 ceramics were evaluated as a function of variable Fe-content (0–5 wt%). X-ray diffraction measurements coupled with Rietveld refinement analyses indicate that the BT, BCT8, and Fe-BCT8 ceramics crystallize in single phase tetragonal structure. Phase transformation occurs with higher Fe doping; Fe-BCT8 ceramics with 5 wt% Fe exhibits fully transformed orthorhombic structure. The crystal structure and phase formation of these ceramics was further confirmed by the Raman spectroscopic (RS) measurements. The RS data coupled with high-resolution X-ray photoelectron spectroscopic (XPS) analyses also confirm the formation of single phase materials without any presence of secondary or impurity phases. Microstructure imaging analyses indicate that the grain size was ∼1 μm, while agglomeration and inhomogeneous distribution were observed with Fe doping. Polarization-electric field (P-E) hysteresis and strain-electric field (S-E) hysteresis measurements revealed the ferroelectric and piezoelectric nature of the ceramics. Ferroelectric and piezoelectric properties were observed to be suppressed for Fe doped BCT8 ceramics due to the partial replacement of Ti4+ by Fe3+ as confirmed by the chemical analyses made using XPS. Temperature dependent dielectric measurements for Fe doped BCT8 show a drastic decrease in ferroelectric Curie temperature (Tc), along with a decrease in dielectric constant compared to that of undoped BCT8. Magnetization (M-H) measurements confirm the presence of long-range magnetic ordering for 5% Fe-doped BCT8 sample. The results demonstrate that addition of 5% Fe in lead-free BCT8 perovskite induces the magnetic ordering and a switchable ferroelectric state, which evidences the presence of multiferroic nature that can be used for four-bit memory and switching applications.
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    Thickness-dependent magnetic and transport properties of La0.5Sr0.5MnO3 thin films deposited by DC magnetron sputtering on the LaAlO3 substrate
    (Springer Verlag, 2018) Yadav, Kamlesh; Singh, H. K.; Maurya, K. K.; Varma, G. D.; Yadav, K.; Singh, H.K.; Maurya, K.K.; Varma, G.D.
    Thickness-dependent structural, magnetic and transport properties of La0.5Sr0.5MnO3 (LSMO) thin films have been studied. A series of the LSMO films with thickness 30, 60, 125 and 300?nm have been deposited on the LaAlO3 substrate using DC magnetron sputtering. The paramagnetic to ferromagnetic transition at TC is followed by antiferromagnetic ordering at TN in all films. It is also found that all LSMO films have TC lower than that of bulk LSMO. A small variation of TC is observed on increasing the film thickness. However, TN is found to rise with increase in the film thickness. The 60?nm-thick film shows a wide insulator to metal transition. The resistivity above 240?K of the films with various thicknesses is consistent with a small polaronic hopping conductivity. The polaronic formation energy EA rises with the increase of the film thickness except for 60?nm thin film, where a small decline in EA is observed. The correlation between observed structural, magnetic and electrical properties with the thickness of the films has been discussed in this paper. ? 2017, Springer-Verlag GmbH Germany, part of Springer Nature.
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    Electronic properties and STM images of vacancy clusters and chains in functionalized silicene and germanene
    (Elsevier B.V., 2017) Jamdagni, Pooja; Kumar, Ashok; Sharma, Munish; Thakur, Anil; Ahluwalia, P. K.
    Electronic properties and STM topographical images of X (=F, H, O) functionalized silicene and germanene have been investigated by introducing various kind of vacancy clusters and chain patterns in monolayers within density functional theory (DFT) framework. The relative ease of formation of vacancy clusters and chain patterns is found to be energetically most favorable in hydrogenated silicene and germanene. F- and H-functionalized silicene and germanene are direct bandgap semiconducting with bandgap ranging between 0.1?1.9?eV, while O-functionalized monolayers are metallic in nature. By introducing various vacancy clusters and chain patterns in both silicene and germanene, the electronic and magnetic properties get modified in significant manner e.g. F- and H-functionalized silicene and germanene with hexagonal and rectangle vacancy clusters are non-magnetic semiconductors with modified bandgap values while pentagonal and triangle vacancy clusters induce metallicity and magnetic character in monolayers; hexagonal vacancy chain patterns induce direct-to-indirect gap transition while zigzag vacancy chain patterns retain direct bandgap nature of monolayers. Calculated STM topographical images show distinctly different characteristics for various type of vacancy clusters and chain patterns which may be used as electronic fingerprints to identify various vacancy patterns in silicene and germanene created during the process of functionalization. ? 2016 Elsevier B.V.