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Pandey S.K.,UGC-DAE Consortium for Scientific Research
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The electronic and magnetic properties of Sr2CoO4 compound have been studied using ab initio electronic-structure calculations. As opposed to a generalized gradient approximation (GGA) calculation, which gives ferromagnetic metallic solution, GGA+U calculations provide two kinds of ferromagnetic solutions: (i) half-metallic and (ii) metallic. The half-metallic solution is a ground state of the system and the metallic one is a metastable state. The strong hybridization between Co3d and O2p orbitals decides the electronic and magnetic properties of the compound. The total magnetic moment per formula unit is found to be ∼3 μB (S=3/2). Our calculations give the magnetocrystalline anisotropy energy of ∼2.7 meV, which provides a good description of experimentally observed large magnetocrystalline anisotropy. The Heisenberg exchange parameters up to fourth nearest neighbors are also calculated. The mean-field theory gives TC =887 K. The possible physical implications of the ferromagnetic half-metallic ground state are also discussed. © 2010 The American Physical Society.


Gupta S.,Indian Institute of Technology Bombay | Rawat R.,UGC-DAE Consortium for Scientific Research | Suresh K.G.,Indian Institute of Technology Bombay
Applied Physics Letters | Year: 2014

Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with negligible hysteresis loss have been observed in ErNiSi compound, which undergoes metamagnetic transition at low temperatures. Magnetization, heat capacity, and resistivity measurements confirm the metamagnetic transition. Both MCE and MR follow H2 dependence in the paramagnetic regime. The maximum value of isothermal entropy change (Δ SM) and MR for a field change of 50 kOe are found to be 19.1 J/kg K and ∼ 34%, respectively. Large MCE with negligible magnetic hysteresis loss could make this material promising for low temperature magnetic refrigeration. © 2014 AIP Publishing LLC.


Okram G.S.,UGC-DAE Consortium for Scientific Research
AIP Advances | Year: 2012

We have reinvestigated the thermopower of group VB metals in polycrystalline forms in the temperature range of 6-300K, taking into account the critical nature of the sample surface and heat treatment especially for niobium. Strikingly small magnitude, negative sign, phonon drag dip and superconductivity not reported previously were observed in surface-cleaned single crystalline Nb. However, while thermopower magnitudes are small, mixed signs were found in the polycrystalline V, Nb and Ta samples. These properties were therefore interpreted as their intrinsic properties and were briefly discussed taking into account of the existing theory by fitting also the data that give the Fermi energies of 10.94 eV, 5.08 eV and 1.86eV, respectively. Copyright © 2012 Author(s).


Dhaka R.S.,UGC-DAE Consortium for Scientific Research | Barman S.R.,UGC-DAE Consortium for Scientific Research
Physical Review Letters | Year: 2010

Aluminum bulk, surface, and multiple plasmons have been observed in the core-level spectra of rare gas (Ne, Ar, and Xe) nanobubbles in Al, whose intensities are even higher than those of Al metal. Both intrinsic and extrinsic bulk plasmons are detected, but they exhibit diametrically opposite intensity variation due to change in the size and implantation depth of the bubbles. Furthermore, the existence of bubble surface plasmon is demonstrated. © 2010 The American Physical Society.


Mishra A.K.,UGC-DAE Consortium for Scientific Research | Das D.,UGC-DAE Consortium for Scientific Research
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2010

Zn 1-xFe xO (x = 0.03, 0.05 and 0.07) nanoparticles synthesized by a chemical route were characterized by different techniques. The structural characterization by XRD and TEM confirmed the phase purity of the samples and indicated a reduction in particle size with increase in the dopant (Fe) concentration in ZnO. The optical characterization of the nanoparticles by FTIR, PL and UV-visible spectroscopy confirmed the formation of wurtzite structure and incorporation of Fe in the ZnO lattice. Magnetization measurements by VSM and Faraday balance techniques indicate presence of room temperature ferromagnetism in the Fe-doped ZnO samples. Local environment around the Fe atoms has been probed by 57Fe Mössbauer spectroscopy and the measured isomer shifts confirmed the charge state of iron as Fe 3+. Positron annihilation lifetime spectroscopy (PALS) measurements confirm the presence of cation vacancies in the nanoparticles and indicate a reduction of overall defect concentration with incorporation of Fe atoms in the ZnO structure. © 2010 Elsevier B.V. All rights reserved.

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