Browsing by Author "P. Shahi"

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Clonal variability and its relevance in generation of new pathotypes in the spot blotch pathogen, Bipolaris sorokiniana
(2008) Shree P. Pandey; Sandeep Sharma; R. Chand; P. Shahi; A.K. Joshi
Spot blotch pathogen Bipolaris sorokiniana of wheat was investigated with threefold objectives: to establish a relationship between morphological and pathological variability of isolates, identify clonal genotype(s) acting as a source for the generation of new variability, and to determine the mechanism of generation of such variability in the pathogen. Isolates were collected from the leaves and seeds of field-grown wheat crop at four different sites in eastern Gangetic plains of India. Eighty-six clonal isolates derived from a single isolate (gray with white patches, Group III), which segregated in an equal proportion of parental and nonparental types, were studied. Morphological characters-i.e., colony morphology, growth rate, and sporulation-were studied along with disease-causing ability of the isolate clones. Clonal isolates were grouped into three categories. Microscopic analysis of nuclei was done to determine the causes of such variability. Morphological variability appeared to be related to the pathological variability. The isolate having epidemic potential appeared different than that acting as the reservoir for variability. The cause of such variability could be attributed either to hyphal fusion and heterokaryosis, nuclear migration and occurrence of multinucleate state, or a combination of these factors. Random Amplified Polymorphic DNA (RAPD) assay suggested that the unique fragments for different groups could be utilized as molecular markers to identify the isolates of specific groups. © 2007 Springer Science+Business Media, LLC.
Correlation between changeover from weak antilocalization (WAL) to weak localization (WL) and positive to negative magnetoresistance in S-doped Bi1.5Sb0.5Te1.3Se1.7
(American Institute of Physics Inc., 2022) Mahima Singh; Labanya Ghosh; Vinod K. Gangwar; Yogendra Kumar; Debarati Pal; P. Shahi; Shiv Kumar; Sudip Mukherjee; K. Shimada; Sandip Chatterjee
The magneto-transport and angle-resolved photoelectron spectroscopy (ARPES) of the S-doped Bi1.5Sb0.5Te1.3Se1.7 system have been investigated. Both the positive magnetoresistance (pMR) and negative magnetoresistance (nMR) under a perpendicular magnetic field as well as a changeover from weak antilocalization (WAL) to weak localization (WL) are observed. The interplay between pMR and nMR is elucidated in terms of the dephasing and spin-orbit scattering time scales. The topological surface state bands have been explored using ARPES. © 2022 Author(s).
Effect of chemical pressure at the boundary of mott insulator to itinerant electron limit transition in spinel vanadates
(American Scientific Publishers, 2015) P. Shahi; A. Kumar; Rahul Singh; Ripandeep Singh; P.U. Sastry; A. Das; Amish G. Joshi; A.K. Ghosh; A. Banerjee; Sandip Chatterjee
The effect of chemical pressure on the structural, transport, magnetic and electronic properties of ZnV2O4 has been investigated by doping Mn and Co onto the Zn sites of ZnV2O4. With Mn doping the V-V distance increases and with Co doping it decreases. The resistivity and thermoelectric power data indicate that, as the V-V distance decreases, the system moves towards quantum phase transition. The transport data also indicate that the conduction is due to small polaron hopping. The chemical pressure shows a non-monotonous behaviour of charge gap and activation energy. On the other hand, when Ti is doped on the V-site of ZnV2O4, the metal-metal distance decreases and, at the same time, TN also increases. © 2015 by American Scientific Publishers.
Effect of Pr- and Nd-doping on structural, dielectric, and magnetic properties of multiferroic Bi0.8La0.2Fe 0.9Mn0.1O3
(American Institute of Physics Inc., 2014) Rahul Singh; G.D. Dwivedi; P. Shahi; D. Kumar; Om Prakash; A.K. Ghosh; Sandip Chatterjee
Bi0.8La0.15RE0.05Fe0.9Mn 0.1O3 (where RE = Pr and Nd) have been prepared via conventional solid state route. The Rietveld refinement of X-ray diffraction patterns shows that both systems crystallize in orthorhombic Pnma space group. Raman modes observed for these two systems indicate that both systems are very close to orthorhombic Pnma structure. Appearance of prominent A1-3 and weak E-2 modes in Bi0.8La0.15Nd0.05Fe 0.9Mn0.1O3 indicate the presence of chemically more active Bi-O covalent bonds (which favors stereochemical activity of Bi lone pair electrons) in comparison to Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. Moreover, Bi 0.8La0.15Nd0.05Fe0.9Mn 0.1O3 system shows higher dielectric constant, low dielectric loss, and higher magnetization value in comparison to Bi 0.8La0.15Pr0.05Fe0.9Mn 0.1O3 system. Ferroelectric transition temperature decreases to 460 °C for both systems in comparison to 710 °C of Bi 0.8La0.2Fe0.9Mn0.1O3. The improved dielectric and magnetic response suggests Bi0.8La 0.15Nd0.05Fe0.9Mn0.1O3 a better multiferroic system than Bi0.8La0.15Pr 0.05Fe0.9Mn0.1O3. © 2014 AIP Publishing LLC.
Effect of y doping on magnetic and transport properties of La 0.7Sr0.3CoO3
(2013) G.D. Dwivedi; K.K. Shukla; P. Shahi; O.K. Jha; A.K. Ghosh; A.K. Nigam; Sandip Chatterjee
The temperature variation of magnetization, resistivity and thermo electric power of undoped and Y-doped La0.7Sr0.3CoO3 samples have been investigated. Y-doping decreases the magnetization possibly due to the spin state transition of Co-ions. The low temperature conduction in (La1-yYy)0.7Sr0.3CoO3 is consistent with the variable range hopping. With Y doping, value of the Seebeck coefficient increases, as Y doping decreases bandwidth and increases distortion. © 2013 American Institute of Physics.
Effect of Y-doping on the transport and magnetic properties of La 0.5Sr0.5CoO3 and La0.7Sr 0.3CoO3
(2013) G.D. Dwivedi; K.K. Shukla; P. Shahi; A.K. Ghosh; A.K. Nigam; Sandip Chatterjee
The temperature variation of magnetization, resistivity, and thermoelectric power of undoped and Y-doped La0.7Sr0.3CoO3 and La0.5Sr0.5CoO3 samples have been investigated. Y-doping decreases the magnetization possibly due to the spin-state transition of Co ions. The low temperature conduction in (La 1-y Y y )0.7Sr0.3CoO3 is consistent with the variable range hopping. With Y-doping, value of the Seebeck coefficient increases as Y-doping decreases bandwidth and increases distortion. Seebeck coefficient value also reflects that the orbital stability increases with Sr concentration. © 2012 Springer Science+Business Media New York.
Enhancement in power factor due to anti-correlation between electrical conductivity and thermoelectric power and induced magnetic ordering in high mobility Zn doped Bi2Te3 topological insulator
(Elsevier Ltd, 2018) Abhishek Singh; P. Shahi; A.K. Ghosh; J.G. Cheng; Sandip Chatterjee
Electrical resistivity, thermoelectric power, magnetotransport and magnetization of Zn doped Bi2Te3 Topological Insulator were studied. Electrical conductivity is enhanced at higher Zn concentration, and the carrier mobility estimated from Hall data reaches a remarkable value of ∼7200 cm2 V-1S−1. Large positive magnetoresistance (MR∼400%) is observed in high mobility samples. Interestingly it is found that the coupling between electrical conductivity and Seebeck coefficient is broken for higher Zn doped Bi2Te3 samples which effectively enhances the thermoelectric power factor (from 2.1mW/K2m for Bi2Te3 to 4.64mW/K2m for Zn doped Bi2Te3). © 2017 Elsevier B.V.
Existence of the multiferroic property at room temperature in Ti doped CoFe 2O 4
(2012) G.D. Dwivedi; Amish G. Joshi; H. Kevin; P. Shahi; A. Kumar; A.K. Ghosh; H.D. Yang; Sandip Chatterjee
The appearance of ferroelectricity has been observed in magnetically ordered Co(Fe 1-xTi x) 2O 4 at room temperature. Magnetization and dielectric constant is found to increase with Ti doping. It is observed from an X-ray Photoemission Spectroscopy study that Ti goes to the octahedral site with (4) ionic state. An MH hysteresis curve at room temperature shows the ferrimagnetic ordering and a PE loop at room temperature clearly indicates the existence of ferroelectricity. © 2011 Elsevier Ltd. All rights reserved.
Magnetic and optical properties of Fe doped crednerite CuMnO2
(Royal Society of Chemistry, 2015) Kaushal K. Shukla; P. Shahi; S. Gopal; A. Kumar; A.K. Ghosh; Ripandeep Singh; Neetika Sharma; A. Das; A.K. Sinha; Amish G. Joshi; A.K. Nigam; Sandip Chatterjee
A geometrically frustrated magnetic CuMnO2 system has been investigated because of its rich magnetic properties. Neutron diffraction, synchrotron X-ray, magnetic, X-ray photoemission spectroscopy (XPS) and UV-Visible spectroscopy measurements have been carried out on CuMnO2 and 5% Fe doped CuMnO2 samples. Fe doping reduces the distortion. Moreover, Fe doping induces the ferromagnetic coupling between ab planes. The value of magnetization is increased with Fe doping but coercivity is decreased. These might be due to the direct Mn-Mn exchange and Mn-O-Cu-O-Mn super-super exchange interactions. The UV-Vis data indicate the appearance of new energy bands in these compounds. The XPS study indicates that Fe is in the 3+ state. © The Royal Society of Chemistry.
Neutron diffraction study of multiferroic Mo-doped CoFe2O4
(Elsevier, 2015) A. Das; G.D. Dwivedi; Poonam Kumari; P. Shahi; H.D. Yang; A.K. Ghosh; Sandip Chatterjee
Neutron diffraction measurements have been carried out to study the coexistence of magnetic ordering and ferroelectricity at room temperature in CoFe1.8Mo0.2O4. It is observed from this study that the Mo6+ preferentially occupies the octahedral site and it converts some of the Fe3+ ions into Fe2+ ions in the tetrahedral site. The conversion of Fe3+ ions into Fe2+ ions modulate the Fe-Fe distances which in effect induce the ferroelectricity in magnetically ordered CoFe1.8Mo0.2O4. © 2014 Elsevier B.V. All rights reserved.
Raman effect and magnetic properties of doped TbMnO3
(2013) A. Kumar; P. Shahi; S. Kumar; K.K. Shukla; Ranjan Kr Singh; A.K. Ghosh; A.K. Nigam; Sandip Chatterjee
The room temperature Raman scattering, structural and temperature variation of magnetic properties of Y- and Ni-doped TbMnO3 are investigated. Both for Y and Ni doping, the Néel temperature (TN) decreases. Y doping reduces effectively both the JTb-Tb and JMn-Mn exchange interactions, whereas Ni doping on the Mn site decreases only the JMn-Mn exchange interaction. The reduction in TN in the Ni-doped sample cannot be explained with simple exchange integral. It might be the case that Ni2+ doping changes the polarization flop observed in TbMnO3 which in effect may change the exchange interaction. In the room temperature Raman spectra for TbMnO3 and Y-doped TbMnO 3 eight modes are observed. When Ni is doped, modes due to MnO 6 bending and in-plane O2 stretching broaden and few modes disappear due to the induced lattice disorder. © 2013 IOP Publishing Ltd.
Role of ion beam excitations on quasi one-dimensional magnetic system of Mn-doped LiCuVO4
(Elsevier Ltd, 2015) Abhishek Kumar; G.D. Dwivedi; Shiv Kumar; P. Shahi; K.K. Shukla; A.K. Ghosh; K. Asokan; D. Kanjilal; R.K. Singh; A.K. Nigam; Sandip Chatterjee
Abstract Induction of short range ferromagnetic ordering has been observed in the quasi one dimensional antiferromagnetic LiCuVO4 system with doping of Mn in the octahedral (Cu) site. Though, magnetic ordering is not stable enough as further increase of Mn-concentration, magnetic ordering gets deteriorated. This might be the case that Mn2+ ions, with strong magnetic moment as compared to Cu2+ ions, enhance the ferromagnetic coupling between the nearest neighbor atoms of quasi-one-dimensional magnetic LiCuVO4 system. Ferromagnetic ordering in LiCu0.95Mn0.05VO4 system also degraded after high energy ion beam excitation which creates defects and may disturb the short range ferromagnetic ordering in its near locality but it does not have much effect on the long range antiferromagnetic ordering. Irradiation causes no change in Raman modes of LiCu0.95Mn0.05VO4 system, while it produces some new vibrational modes in intermediate and high frequency region of LiCu0.9Mn0.1VO4 system. Above results have been understood based on competitions between ferromagnetic nearest neighbor (NN) coupling and antiferromagnetic next nearest neighbor (NNN) coupling in CuO2 chain. © 2015 Elsevier B.V.
Signature of ferroelectricity in magnetically ordered Mo-doped CoFe 2O4
(2010) G.D. Dwivedi; K.F. Tseng; C.L. Chan; P. Shahi; J. Lourembam; B. Chatterjee; A.K. Ghosh; H.D. Yang; Sandip Chatterjee
Coexistence of both magnetic ordering and ferroelectricity (with giant dielectric constant) have been observed for the first time in Co(Fe 1-xMox)2O4. The magnetization of Co(Fe1-xMox)2O4 ranges from 0 to 0.1) was found to increase with doping concentration of Mo. The magnetic properties indicate that Mo goes into the tetrahedral site. The giant dielectric constant may be attributed to the Maxwell-Wagner relaxation mechanism. © 2010 The American Physical Society.
Simultaneous presence of ferroelectricity and magnetism in Mo-doped CoFe2O4
(2010) G.D. Dwivedi; K.F. Tseng; C.L. Chan; P. Shahi; B. Chatterjee; A.K. Ghosh; H.D. Yang; Sandip Chatterjee
Signature of ferroelectricity has been observed for the first time in magnetically ordered Co(Fe1-xMox)2O 4. The structural property of Co(Fe1-xMox) 2O4 (x ranges from 0 to 0.1) indicates that Mo goes into the tetrahedral site. The frequency dependent P-E loop indicates the existence of weak ferroelectricity in Mo-doped CoFe2O4. © 2010 American Institute of Physics.
Structural and magnetic properties of quasi-one-dimensional doped LiCuVO4
(2013) Abhishek Kumar; Poonam Kumari; A. Das; G.D. Dwivedi; P. Shahi; K.K. Shukla; A.K. Ghosh; A.K. Nigam; K.K. Chattopadhyay; Sandip Chatterjee
The Neutron diffraction, X-ray photoemission and Magnetic properties of Zn, Co and Mn-doped LiCuVO4 were investigated. Both with Zn and Co doping the antiferromagnetic correlation increase. On the other hand Mn-doping induces the short range ferromagnetic ordering. Neutron diffraction study does not show any phase transition down to 5 K i.e., there is no indication of long range magnetic ordering. Neutron diffraction study also indicates that with Zn, Co and Mn doping the V-O lengths are changed. Maximum change in the V-O distances is observed for Mn-doped sample. On the other hand, X-ray photoemission spectroscopic data indicates Mn doping converts some Cu 2+ ions into Cu3+ ions. © 2013 Published by Elsevier Inc.