Browsing by Author "G.D. Dwivedi"

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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 Sr-doping on multiferroic properties of Bi 0.8La 0.2Fe 0.9Mn 0.1O 3
(2012) Anup K. Ghosh; H. Kevin; B. Chatterjee; G.D. Dwivedi; A. Barman; H.D. Yang; S. Chatterjee
The effect of Sr-doping on ferroelectricity and ferromagnetism at room temperature has been studied for Bi 0.8La 0.2Fe 0.9Mn 0.1O 3 ceramic system. X-ray diffraction shows that a structural phase transition occurs from rhombohedral structure of BiFeO 3 (space group R3c) to orthorhombic structure of Bi 0.8La 0.2FeO 3 (space group C222). Substitutions of Sr-ions in Bi-site and Mn-ions in Fe-site do not induce any further structural change. Moreover, doping of Sr-ions plays a crucial role to obtain single phased samples. DTA and TGA studies show that both the magnetic transition temperature ( TM) and the ferroelectric transition temperature ( TC) decrease for Bi 0.7Sr 0.1La 0.2Fe 0.9Mn 0.1O 3. Sr-doping enhances the ferroelectric property by increasing the electric polarization. MH measurement shows that Sr-ions partially destroy the spin cycloidal structure in it giving rise to weak ferromagnetism (nonlinearity) at room temperature. © 2011 Elsevier Ltd. All rights reserved.
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.
Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases
(American Institute of Physics Inc., 2016) G.D. Dwivedi; Amish G. Joshi; Shiv Kumar; H. Chou; K.S. Yang; D.J. Jhong; W.L. Chan; A.K. Ghosh; Sandip Chatterjee
X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum. © 2016 Author(s).
Enhancement of ferromagnetic and ferroelectric properties in codoped biFeO3
(Chemical Publishing Co., 2011) B. Chatterjee; H. Kevin; G.D. Dwivedi; H.D. Yang; S. Chatterjee; A.K. Ghosh
Co-doped insulating Bi0.8La0.2Fe 1-xMnxO3, (x = 0, 0.1) ceramics were prepared by conventional solid state reaction method. The XRD study shows that 20 % substitution of La ions changes the structure from rhombohedral (space group R3c) that of BaFeO3 to the orthorhombic (C222) for Bi0.8La 0.2FeO3 (BLFO). For further substitution of Mn-ions in Fe-site no structural change occurs. From DTA and TGA study, it is observed that magnetic transition temperature (Tm) decreases appreciably whereas ferroelectric transition temperature (TC) does not affect much with the increase of Mn-concentration. The magnetization-magnetic field measurements show that increase of magnetization for co-doping of La and Mn in Bi 0.8FeO3 is due to the destruction of the spin cycloid structure in it and the introduction of the mixed valance state. P-E measurement shows the ferroelectric nature of the sample.
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.
Magneto-dielectric coupling and transport properties of the ferromagnetic-BaTiO3 composites
(American Institute of Physics Inc., 2015) Manish Kumar; S. Shankar; G.D. Dwivedi; A. Anshul; O.P. Thakur; Anup K. Ghosh
Ferromagnetic and large magnetoresistance (MR) nanocomposites of La0.67Sr0.33MnO3-BaTiO3 (LSMO-BTO) are synthesized via sol-gel route. The X-ray diffraction confirms the existence of two chemically separated phases in the composites. The maximum MR (35%) was achieved in LSMO-5% BTO (LB5). The coupling between the coexisting phases is observed from the dielectric anomaly at the ferromagnetic transition (Tc = 353 K) for LB5 composition. We observed maximum magnetodielectric effect at Tc of 1.18% in magnitude for LB5 and the effect of magnetic field on other composites was significant. These results are related to the large spin polarization within grains as well as at the grain boundaries and the evidence of variation in dielectric parameters with magnetic field reveal the magnetoelectric coupling in LSMO-BTO nanocomposites. © 2015 AIP Publishing LLC.
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.
Observation of the multiple magnetic phases in double perovskite Pr1.8La0.2CoFeO6
(Elsevier B.V., 2024) Dheeraj Kumar; Prajyoti Singh; Mohd Alam; Satya Vijay Kumar; Srishti Dixit; Krishanu Bandyopadhyay; G.D. Dwivedi; Satyen Saha; A.K. Ghosh; Sandip Chatterjee
The structural and magnetic properties of the double perovskite Pr1.8La0.2CoFeO6 have been investigated. The X-ray diffraction study shows that the system acquires room-temperature orthorhombic phase with the Pnma space group. The X-ray photoemission spectroscopy (XPS) measurement confirmed that the B-site ions are present in mixed valence states i.e. Co has been found in Co2+ and Co3+ valance states whereas Fe has been found in Fe3+/Fe4+. Magnetic measurements of the system confirm the existence of several fascinating magnetic behaviors, such as long-range canted antiferromagnetism withTN ∼ 271 K, giant exchange bias, and re-entrant cluster glass phase (TG ∼ 33 K). Field-dependent magnetization shows a large spontaneous exchange bias; HSEB∼ 1.8 kOe and giant conventional exchange bias, HCEB∼ 2.4 kOe at 5 K. Antiferromagnetic materials with large exchange bias can be utilized in high-density spintronic devices. Temperature-dependent Raman study demonstrates that the observed phonon mode exhibits anomalous behavior close to the magnetic transition temperature. Analysis of anomalous softening of phonon mode below TN, clarifies the presence of significant spin-phonon coupling while the magnetostriction effect does not play any significant role in the observed phonon anomaly. © 2024
Particle size dependence on the structural, transport and optical properties of charge-ordered Pr0.6Ca0.4MnO3
(Elsevier Ltd, 2015) Satyam Kumar; G.D. Dwivedi; J. Lourembam; Shiv Kumar; U. Saxena; A.K. Ghosh; H. Chou; Sandip Chatterjee
Abstract Structural, transport and optical properties of nano-crystalline Pr0.6Ca0.4MnO3 have been investigated to emphasize on the semiconducting properties of charge-ordered manganite. Rietveld refinement of X-ray diffraction pattern of Pr0.6Ca0.4MnO3 nanoparticles show that due to increase in sintering temperature, MnO6 octahedra elongated along z-direction and compressed in x-y plane. Both Mn-O-Mn angles are found to decrease with increasing sintering temperature. Fourier transform infrared (FTIR) spectroscopy measurements reveal that the stretching and bending vibration of Mn-O-Mn is responsible for the change in Mn-O-Mn bond length and bond angle respectively. With increasing sintering temperature, these vibrations tend to increase, which resulted in the further distortion of MnO6 octahedra. Magnetic measurements suggest that charge ordering is established and system becomes antiferromagnetic with increasing particle size. Resistivity behavior of Pr0.6Ca0.4MnO3 nanoparticles clearly exhibit semiconducting nature of these systems, which is due to the formation of charge-ordered state of Mn3+ and Mn4+. Estimated optical band-gap of ∼3.7 eV for Pr0.6Ca0.4MnO3 nanocrystals, makes it a potential candidate for wide band-gap magnetic semiconductors. © 2015 Published by Elsevier B.V.
Probing the Griffiths like phase, unconventional dual glassy states, giant exchange bias effects and its correlation with its electronic structure in Pr2-xSrxCoMnO6
(Institute of Physics Publishing, 2020) Arkadeb Pal; Prajyoti Singh; V.K. Gangwar; Amish G Joshi; P. Khuntia; G.D. Dwivedi; Prince K. Gupta; Mohd Alam; Khyati Anand; K. Sethupathi; Anup K. Ghosh; Sandip Chatterjee
Crystal, electronic structure, dc and ac magnetization properties of the hole substituted (Sr2+) and partially B-site disordered double perovskite Pr2-xSrxCoMnO6 system have been investigated. The XRD pattern analysis showed a systematic decrease in the lattice parameters owing to the enhanced oxidation states of the Co/Mn ions. The electronic structure study by XPS measurements suggested the presence of mixed valence states of the B-site ions (Co2+ /Co3+ and Mn3+ /Mn4+) with significant enhancement of the average oxidation states due to hole doping. The mere absence of electronic states near the Fermi level in the valence band (VB) spectra for both pure (x = 0.0) and Sr doped (x = 0.5) systems indicated the insulating nature of the samples. Sr substitution is observed to increase the spectral weight near the Fermi level suggesting for an enhanced conductivity of the hole doped system. The dc magnetization data divulged a Griffiths like phase above the long-range ordering temperature. A typical re-entrant spin glass like phase driven by the inherent anti-site disorder (ASD) has been recognized by ac susceptibility study for both the pure and doped systems. Most interestingly, the emergence of a new cluster glass like phase (immediately below the magnetic ordering temperature and above the spin-glass transition temperature) solely driven by the Sr substitution has been unravelled by ac magnetization dynamics study. Observation of these dual glassy states in a single system is scarce and hence placed the present system amongst the rare materials. The isothermal magnetization measurements further probed the exhibition of the giant exchange bias effect originated from the interfacial exchange interactions due to existence of low temperature antiferromagnetic clusters embedded in the glassy matrix. © 2020 IOP Publishing Ltd.
Role of codoping on multiferroic properties at room temperature in BiFeO3 ceramic
(Elsevier Ltd, 2013) Anup K. Ghosh; G.D. Dwivedi; B. Chatterjee; B. Rana; A. Barman; S. Chatterjee; H.D. Yang
Role of codoping (20% La in Bi-site and 10% Mn in Fe-site) on mutiferroic properties in insulating BiFeO3 ceramic have been investigated. The X-ray diffraction (XRD) with Rietveld refinement shows that the structure of Bi0.8La0.2FeO3 is orthorhombic (Pnma). Furthermore, it shows that on substitution of 10% Mnions in Fe-site, no structural change occurs which has been supported by micro-Raman study. DTA study shows that ferroelectric transition temperature (TC) decreases very fast due with La-doping and slowly with the Mn-doping. Measurement on magnetization vs. applied magnetic field (M-H) shows increase of magnetization due to codoping of La and Mn in BiFeO 3. This may be due to partly destruction or suppression of the spin cycloid structure in it and/or the introduction of the mixed valance state. P-E measurement shows high leakage in Bi0.8La0.2Fe0.9Mn0.1O3. © 2013 Elsevier Ltd. All rights reserved.
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.
Signature of Griffith phase in (Tb1-xCex)MnO3
(American Institute of Physics Inc., 2016) Abhishek Kumar; G.D. Dwivedi; A. Singh; R. Singh; K.K. Shukla; H.D. Yang; A.K. Ghosh; Sandip Chatterjee
Griffith phase phenomena is attributed to existence of FM (ferromagnetic) cluster in AFM (antiferromagnetic) ordering which usually occurs in ferromagnetic and antiferromagnetic bilayers or multilayers. In (Tb1-xCex)MnO3 evolution of Griffith phase have been observed. The observed Griffith phase might be due to the exchange interaction between Mn3+/Mn2+ states. © 2016 Author(s).
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.
Structural, magnetic, magneto-transport properties, and electronic structure study of charge-ordered (La0.4Pr0.6)0.65Ca0.35MnO3
(Elsevier Ltd, 2017) G.D. Dwivedi; Satyam Kumar; Amish G. Joshi; Shiv Kumar; A.K. Ghosh; H. Chou; H.D. Yang; Sandip Chatterjee
Structural, magnetic and magneto-transport properties of nanocrystalline (La0.4Pr0.6)0.65Ca0.35MnO3have been investigated along with their electronic structures. Temperature dependent magnetization measurement shows different magnetic phases in different temperature regions. (La0.4Pr0.6)0.65Ca0.35MnO3completely transforms into a ferromagnet below 50 K. The temperature dependent resistivity measurement of (La0.4Pr0.6)0.65Ca0.35MnO3system displays semiconducting behavior up to 45 K under zero magnetic field. Application of 1 T magnetic field enforces semiconductor to metal transition around 65 K during cooling and around 115 K during warming. This shows that (La0.4Pr0.6)0.65Ca0.35MnO3still behaves as itinerant ferromagnet under applied magnetic field. X-ray photoemission spectra of Mn2p and Mn3s core-level confirm dual valence states of Mn (Mn3+and Mn4+), which is responsible for the magnetic behavior of the (La0.4Pr0.6)0.65Ca0.35MnO3system. High-resolution ultraviolet photoemission spectra near Fermi-edge confirms the presence of finite electronic states at Fermi-level, which explains the observed low-temperature metallic behavior of the (La0.4Pr0.6)0.65Ca0.35MnO3system. © 2016
Structural, transport and optical properties of (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals: A wide band-gap magnetic semiconductor
(Royal Society of Chemistry, 2015) Satyam Kumar; G.D. Dwivedi; Shiv Kumar; R.B. Mathur; U. Saxena; A.K. Ghosh; Amish G. Joshi; H.D. Yang; Sandip Chatterjee
(La0.6Pr0.4)0.65Ca0.35MnO3 system has been synthesized via a sol-gel route at different sintering temperatures. Structural, transport and optical measurements have been carried out to investigate (La0.6Pr0.4)0.65Ca0.35MnO3 nanoparticles. Raman spectra show that Jahn-Teller distortion has been decreased due to the presence of Ca and Pr in A-site. Magnetic measurements provide a Curie temperature around 200 K and saturation magnetization (MS) of about 3.43μB/Mn at 5 K. X-ray photoemission spectroscopy study suggests that Mn exists in a dual oxidation state (Mn3+ and Mn4+). Resistivity measurements suggest that charge-ordered states of Mn3+ and Mn4+, which might be influenced by the presence of Pr, have enhanced insulating behavior in (La0.6Pr0.4)0.65Ca0.35MnO3. Band gap estimated from UV-Vis spectroscopy measurements comes in the range of wide band gap semiconductors (∼3.5 eV); this makes (La0.6Pr0.4)0.65Ca0.35MnO3 a potential candidate for device application. This journal is © The Royal Society of Chemistry 2015.