Udaipur, India
Udaipur, India

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Samariya A.,University of Rajasthan | Singhal R.K.,University of Rajasthan | Singhal R.K.,Brazilian Center for Research in Physics (CBPF) | Kumar S.,Sukhadia University | And 6 more authors.
Materials Chemistry and Physics | Year: 2010

Effect of injection of hydrogen ions, followed by their evaporation, has been investigated in the Zn1-xFexO (x = 0.02-0.07) pellets to throw some light on electronic structure and magnetic correlations. The XRD patterns show that x ≤ 0.05 samples are single phase and the Fe ions incorporate at the Zn2+ sites, while a secondary phase ZnFe 2O4 is detected for x ≥ 0.07. The 2% Fe-doped sample retains a paramagnetic ground state down to 50 K. Likewise, the 5% doped sample also shows paramagnetic state at 300 K but a weak ferromagnetic ordering stems from its cooling (Tc ∼ 160 K). Strikingly, the 5% doped sample, when annealed in hydrogen atmosphere, showed inducement of room temperature ferromagnetism. More significantly, the hydrogen-induced magnetism disappears upon evaporating the H ions by re-heating the sample. The magnetic ordering and the electronic properties exhibit a close parallelism/interplay. The X-ray photoemission spectroscopy results testify the Fe to be in mixed valent state (>2+) in paramagnetic state, however, the ferromagnetic transition stems only upon Fe3+ reducing to Fe2+, accompanied by emergence of oxygen vacancies as a parallel electronic phenomenon. Origin of H-mediated ferromagnetism is discussed in the framework of cationic vs. anionic vacancies and it is suggested that oxygen vacancies play major role in mediating the coupling. © 2010 Elsevier B.V. All rights reserved.


Singhal R.K.,University of Rajasthan | Samariya A.,University of Rajasthan | Kumar S.,Sukhadia University | Xing Y.T.,Brazilian Center for Research in Physics (CBPF) | And 4 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2010

The electronic structure and magnetic properties of cobaltdoped (7.5%) and manganese co-doped (2.5%) ZnO polycrystalline samples have been investigated to understand the mechanism of room temperature ferromagnetism (RTFM) in dilute magnetic semiconductors. The samples in powder form were annealed in argon and hydrogen atmospheres followed by their repressing into pellets and reheating in air. Rietveld analysis of X-ray diffraction patterns confirmed the singlephase nature of the samples in the wurtzite type hexagonal (P6 3mc) ZnO structure. The X-ray photoelectron spectroscopy (XPS) results indicate that the Co and Mn atoms are in +2 oxidation states, which incorporate at the Zn 2+ site, with no signature of metallic clusters. The Co-doped sample prepared in air displays a paramagnetic state while the sample annealed in Ar atmosphere shows a weak ferromagnetic ordering at 300 K. The co-doping of Mn further enhances the ferromagnetic ordering, indicating that Co andMnions play an additive role in inducing the ferromagnetic ordering in the ZnO matrix. Interestingly, the Co- and (Co+Mn)-doped ZnO samples annealed in hydrogen atmosphere show a huge increment in the magnetic moment, however, the Mn ions seem to stay passive towards the hydrogen induced magnetization. Notably, the samples reheated in air show suppression of the induced ferromagnetism (FM). The resistance measurements suggest that the additional carriers induced upon hydrogenation also play some role in mediating the exchange coupling. The O 1s XPS and the XRD results show clear evidence of oxygen depletion in the samples upon hydrogenation, followed by a recovery upon their reheating in air. The observed FM is explained in terms of composite effect of the oxygen vacancies and the carrier density. Our results point out that the ferromagnetic ordering could be switched between 'on' and 'off' by introducing (through hydrogenation) and by removing (through reheating in air) the oxygen vacancies in Co-doped ZnO. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Singhal R.K.,University of Rajasthan | Singhal R.K.,Brazilian Center for Research in Physics (CBPF) | Samariya A.,University of Rajasthan | Xing Y.T.,Brazilian Center for Research in Physics (CBPF) | And 5 more authors.
Journal of Physics: Conference Series | Year: 2010

We report the results of electronic and magnetic properties of poly-crystalline Zn1-xMxO (M = Co and Mn) pellets studied by XRD, VSM and XPS. The specimens were synthesized by solid state reaction method using high purity oxides. Samples exhibit Wurtzite hexagonal symmetry and show interesting magnetic properties. The Co (5%) doped sample prepared by heating in air shows a paramagnetic state in agreement with several claims. But the sample prepared by heating in Ar atmosphere depicts ferromagnetic ordering. Addition of 2% Mn in it further enhances its magnetic moment. The specimens ZnCoO (Ar heated) and ZnCoMnO were hydrogenated at 550°C that caused a significant change in their magnetization. The Co doped ZnO shows a robust increment in the magnetic moment but the Mn doping does not seem to respond to hydrogenation. O 1s XPS results show clear evidence of oxygen depletion for the samples prepared by heating in Ar atmosphere and a further depletion upon hydrogenation. Results suggest oxygen vacancies as the basic origin for room temperature ferromagnetism in doped ZnO. © 2010 IOP Publishing Ltd.


Kumar K.,Sukhadia University | Bhatt S.,Sukhadia University | Jani A.R.,Sardar Patel University | Ahuja B.L.,Sukhadia University
Physica B: Condensed Matter | Year: 2015

We present the first-ever experimental Compton profiles (CPs) of ZrSSe2 and ZrS1.5Se1.5 using 100 mCi 241Am Compton spectrometer. To analyze the experimental momentum densities, we have computed for the first-time the CPs, energy bands and density of states using linear combination of atomic orbitals (LCAO) method. To model the exchange and correlation effects within LCAO approach, we have considered Hartree-Fock (HF), density functional theory (DFT) with revised functional of Perdew-Becke-Ernzerhof (PBEsol) and hybridization of HF and DFT. Going beyond computation of electronic properties using LCAO method, we have also derived electronic and optical properties using the modified Becke-Johnson (mBJ) potential within full potential linearized augmented plane wave (FP-LAPW) method. There is notable decrease in the energy band gap on replacing S by Se atoms in ZrSSe2 to obtain ZrS1.5Se1.5 composition, which is mainly attributed to readjustment of Zr-4d, S-3p and Se-4p states. It is seen that the CPs based on hybridization of HF and DFT show a better agreement with the experimental profiles than those based on individual HF and DFT-GGA-PBEsol schemes. The optical properties computed using FP-LAPW-mBJ method unambiguously depict feasibility of using both the sulphoselenides in photovoltaics and also utility of ZrS1.5Se1.5 in the field of non-linear optics. © 2015 Elsevier B.V. All rights reserved.


Mahesh P.,CSIR - Central Electrochemical Research Institute | Catherine J.K.,CSIR - Central Electrochemical Research Institute | Gahalaut V.K.,CSIR - Central Electrochemical Research Institute | Kundu B.,CSIR - Central Electrochemical Research Institute | And 17 more authors.
Gondwana Research | Year: 2012

We analyze GPS data from 26 sites located on the Indian plate and along its boundary. The large spatial coverage of the Indian plate by these sites and longer data duration helped us in refining the earlier estimates of the Euler pole for the Indian plate rotation. Our analysis suggests that the internal deformation of the Indian plate is very low (<1-2mm/year) and the entire plate interior region largely behaves as a rigid plate. Specifically, we did not infer any significant difference in motion on sites located north and south of the Narmada Son failed rift region, the most prominent tectonic feature within the Indian plate and a major source of earthquakes. Our analysis also constrains the motion across the Indo-Burmese wedge, Himalayan arc, and Shillong Plateau and Kopili fault in the NE India. © 2012 International Association for Gondwana Research.


Roy A.B.,Presidency University of India | Chatterjee A.,Presidency University of India | Chauhan N.K.,Sukhadia University
Journal of the Geological Society of India | Year: 2013

Kachchh in western Indian Shield, according to the Bureau of Indian Standard (IS:1893:2002), falls in Seismic Zone V. This is intriguing considering that the region is far away from active Plate margin. Apart from the recent incidences of earthquakes, there are several pre-historic/archaeological records of earthquakes in the region. Beyond these, the geological evidence of earth-movements (causing earthquakes) is provided by the occurrence of several' active' faults, which are considered geological markers of palaeoseismicity. There are records of innumerable incidences of faulting in the region in not so distant geological past. Study of fault features especially the scarp faces marking abrupt change in physical relief proves that the different levels of topography in the entire terrain are fault-bound features. Studies also confirm that the topographic difference between the high and 'sunken' features have formed due to uplift and relative down-sagging during the geomorphotectonic evolution of the terrain. Features that make the region unique are: (i) restriction of fault-related deformation zone to a narrow strip between the southern margin of Thar Desert and the south coast line of the Kachchh Peninsula; (ii) overall sub-horizontality of bedding and other topographic and planation surfaces over the entire region; (iii) evidence of fault-controlled geomorphology indicating vertical movement along fault planes; (iv) evidence constraining the time of geomorphological evolution of the terrain only during the Late Quaternary, making it the youngest neotectonically evolved terrain in the Precambrian Indian Shield. © 2013 Geological Society of India.


Choudhary B.L.,University of Rajasthan | Kumar S.,Sukhadia University | Krishnamurthy A.,University of Rajasthan | Srivastava B.K.,University of Rajasthan
AIP Conference Proceedings | Year: 2013

DC magnetization measurements have been made on two systems with 30 atomic% and 50 atomic% substitutions of Pr for La in the perovskite LaMn 0.8Co0.2O3. The 30 atomic% sample crystallizes in the O* symmetry (c ≥ a ≥ b/√2) and 50 atomic% sample crystallizes in the O' symmetry (a ≥ c ≥ b/√2). Pr Substitution for La in the series La1-xPrxMn0.8Co 0.2O3 leads to contraction of the cell volume. Lattice parameter a increases with Pr substitution while both b and c decrease. The two systems are ferromagnetic. Curie temperature decreases with increasing substitution of Pr showing weakening of ferromagnetism. Departures between magnetization (M) - temperature (T) curves recorded in field cool and zero field cool mode are indicative of magnetic disorder. However, for both the samples the magnetic field (upto 1 kOe) does not show a marked effect on the peak temperature Tm in M - T curves recorded in zero field cooling mode. © 2013 AIP Publishing LLC.


Bhu H.,Sukhadia University | Purohit R.,Government College | Ram J.,Government College | Sharma P.,Government College | Jakhar S.R.,Jai Narain Vyas University
Journal of Earth System Science | Year: 2014

We report site motion of a permanent GPS site at Udaipur (udai), Rajasthan on the Udaipur block of Aravalli Craton. The GPS measurements of 2007-2011 suggest that the site moves at a rate of about 49 mm/year towards northeast. As the site motion is consistent with the predicted plate motion using the estimated euler pole of rotation for the Indian Plate, it implies that there is insignificant internal deformation/strain in the region. Such a deformation is consistent with very low seismic activity in the region. The epicenters of the infrequent low magnitude earthquakes are located on the Precambrian lineaments on the west of Udaipur Block, and on the NW-SE striking younger lineament in the south of the block. © Indian Academy of Sciences.


Ahuja B.L.,Sukhadia University | Mohammad F.M.,University of Tikrit | Mohammed S.F.,University of Tikrit | Sahariya J.,Manipal University India | And 2 more authors.
Journal of Physics and Chemistry of Solids | Year: 2015

A unique applicability of Compton spectroscopy in probing the electronic states of rare earth aluminides using high energy (662 keV) γ-rays is reported. We have measured first-ever Compton profiles of Dy1-xErxAl2 (x=0, 0.2) using 20Ci 137Cs Compton spectrometer. The charge reorganization in Dy1-xErxAl2 (x=0, 0.2), on the formation of compound, has been discussed using the valence band Compton profile data. The experimental Compton profile data unambiguously establish charge transfer from Al to Dy (Dy and Er) on formation of x=0.0 (0.2) compound, which is in tune with spin polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) calculations. A reasonable agreement between SPR-KKR based Compton profiles and the experimental data show applicability of the Green function method in predicting the electronic properties of rare earth compounds. © 2014 Elsevier B.V. All rights reserved.


Mohammed S.F.,University of Tikrit | Mohammad F.M.,University of Tikrit | Sahariya J.,Sukhadia University | Mund H.S.,Sukhadia University | And 2 more authors.
Applied Radiation and Isotopes | Year: 2013

In the present work, we have studied electron momentum density of CaCO3 using a Compton scattering technique. The experiment has been performed using a 100mCi 241Am (59.54keV) Compton spectrometer. The experimental data have been interpreted in terms of theoretical Compton profiles. To compute the theoretical momentum densities, energy bands and density of states, we have used linear combination of atomic orbitals method as embodied in CRYSTAL09 code. We have used local density approximation, generalized gradient approximation (GGA) and second order GGA (SOGGA) within the frame work of density functional theory. It is seen that the GGA gives a better agreement with the experimental data than other approximations. We have also discussed the energy bands and density of states of CaCO3. © 2012 Elsevier Ltd.

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