Browsing by Author "G.S. Okram"

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Effect of EDTA on luminescence property of Eu+3 doped YPO 4 nanoparticles
(2010) A.K. Parchur; G.S. Okram; R.A. Singh; R. Tewari; Lina Pradhan; R.K. Vatsa; R.S. Ningthoujam
Nanoparticles of Eu3+ doped YPO4 have been prepared using ethylene glycol (EG). Ethylene diamine tetra acetic acid (EDTA) is used as a complexing agent. X-ray diffraction results show that the nanoparticles are crystalline in tetragonal structure. Based on William-Hall relation, the effective crystallite size and strain developed in lattice are found to be 28 nm and 0.002, respectively. With the addition of EDTA, there is a slight shift towards the lower wavelength in emission peaks. Asymmetric ratio of electric to magnetic dipole transition intensities are found to decrease with addition of EDTA. Emission intensity decreases with EDTA because of decrease of particle size as well as decrease of number of Eu3+ activators per unit volume. These materials are dispersible in water, which may have potential biological applications. © 2010 American Institute of Physics.
Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator
(Institute of Physics Publishing, 2016) Rahul Singh; K.K. Shukla; A. Kumar; G.S. Okram; D. Singh; V. Ganeshan; Archana Lakhani; A.K. Ghosh; Sandip Chatterjee
Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases. © 2016 IOP Publishing Ltd.
Tuning of carrier type, enhancement of Linear magnetoresistance and inducing ferromagnetism at room temperature with Cu doping in Bi2Te3 Topological Insulators
(Elsevier Ltd, 2018) Abhishek Singh; Rahul Singh; T. Patel; G.S. Okram; A. Lakhani; V. Ganeshan; A.K. Ghosh; S.N. Jha; Swapnil Patil; Sandip Chatterjee
Structural, resistivity, thermoelectric power, magneto-transport and magnetic properties of Cu doped Bi2Te3 topological insulators have been investigated. The tuning of charge carriers from n to p type by Cu doping at Te sites of Bi2Te3 is observed both from Hall effect and thermoelectric power measurements. Carrier mobility decreases with the doping of Cu which provides evidence of the movement of Fermi level from bulk conduction band to the bulk valence band. Thermoelectric power also increases with doping of Cu. Moreover, linear magnetoresistance (LMR) is observed at high magnetic field in pure Bi2Te3 which is associated to the gapless topological surface states protected by time reversal symmetry (TRS). Furthermore, doping of non-magnetic Cu induces ferromagnetism at room temperature and also enhances the magnetoresistance. © 2017