Browsing by Author "D.M. Phase"

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Electronic structure by X-ray absorption spectroscopy and observation of field induced unusually slow spin relaxation from magnetic properties in pyrochlore Eu2−xFexTi2O7
(Elsevier B.V., 2019) Arkadeb Pal; Surajit Ghosh; Shiv Kumar; Eike F. Schwier; Masahiro Sawada; Kenya Shimada; Mukul Gupta; D.M. Phase; A.K. Ghosh; Sandip Chatterjee
X-ray absorption spectroscopy (XAS) and magnetization of hybrid pyrochlore Eu2-xFexTi2O7 (EFTO) were investigated, where the rare earth Eu (4f) was replaced with transition metal Fe (3d) to introduce competing 4f-3d interactions. It is confirmed that the valence states of Eu and Fe ions are formally trivalent while that of Ti ions are tetravalent (3d0). The analysis yielded that the tetravalent Ti ions occupy octahedral sites with distorted Oh symmetry which is triggered by the presence of vacant 8a anionic site adjacent to TiO6 octahedra. Further study with Fe doping revealed that it essentially reduces the octahedral distortion by introducing anionic disorder (migration of 48f oxygen ions to 8a site). Analysis of O K edge XAS spectra further confirmed the Fe substitution causing the systematic change in the ligand (O2−) coordination of the Ti4+ cations. Interestingly, a new field induced transition at low temperature T* (4 K < T* < 8 K) associated with unusually slow spin relaxation was observed. The transition shifted towards higher temperatures both with increasing applied field and Fe concentration. However, the single ion spin freezing (Tf ∼ 35 K) appears to be largely suppressed with Fe substitution. Moreover, dc magnetization data showed rise of ferromagnetic contribution below 100 K. © 2018
Highly efficient field emission properties of radially aligned carbon nanotubes
(Royal Society of Chemistry, 2018) Prashant Tripathi; Bipin Kumar Gupta; Ashish Bhatnagar; C.R.P. Patel; Prashant K. Banker; Dattatray J. Late; Mahendra A. More; N.P. Lalla; D.M. Phase; R.J. Choudhary; M.A. Shaz; P.M. Ajayan; O.N. Srivastava
Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm-1 at 10 μA cm-2), a low threshold field (0.41 V μm-1 at 100 μA cm-2) and a high field emission current density (7.71 mA cm-2 at 0.78 V μm-1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources. © 2018 The Royal Society of Chemistry.
Structural studies of Ni2+x Mn1-x Ga by powder x-ray diffraction and total energy calculations
(2007) S. Banik; R. Ranjan; A. Chakrabarti; S. Bhardwaj; N.P. Lalla; A.M. Awasthi; V. Sathe; D.M. Phase; P.K. Mukhopadhyay; D. Pandey; S.R. Barman
The crystal structure of Ni2+x Mn1-x Ga has been studied as a function of composition (x) by powder x-ray diffraction. For Ni2.24 Mn0.75 Ga, where one-fourth of the Mn atoms are replaced by Ni, the experimentally determined lattice constants are in good agreement with theoretical equilibrium lattice constants calculated by minimization of total energy using full potential linearized augmented plane-wave method. For 0.15≤x≤0.35, a nonmodulated tetragonal martensitic phase is obtained at room temperature, whose lattice constant c increases and a decreases linearly with increasing x following Vegard's law. A 7M modulated monoclinic phase is obtained for x=0.2 due to annealing. The small width of the hysteresis of the martensitic transition shows its thermoelastic nature that is the characteristic of a shape memory alloy. Phase coexistence is observed for 0.1≤x≤0.15 at room temperature, confirming the first-order nature of the martensitic transition. © 2007 The American Physical Society.
X-ray diffraction and photoelectron spectroscopy study of swift heavy ion irradiated Mn/p-Si structure
(Elsevier, 2010) M.K. Srivastava; T. Shripathi; D.M. Phase; P.C. Srivastava
The electronic structure and interfacial chemistry of thin manganese films on p-Si (1 0 0) have been studied by photoelectron spectroscopy measurements using synchrotron radiation of 134 eV and from X-ray diffraction data. The Mn/p-Si structures have been irradiated from swift heavy ions (∼100 MeV) of Fe 7+ with a fluence of 1 × 10 14 ions/cm 2 . Evolution of valence band spectrum with a sharp Fermi edge has been obtained. The observed Mn 3d peak has been related to the bonding of Mn 3d-Si 3sp states. Mn 3p (46.4 eV), Mn 3s (81.4 eV) and Si 2p (99.5 eV) core levels have also been observed which show a binding energy shift towards lower side as compared to their corresponding elemental values. From the photoelectron spectroscopic and X-ray diffraction results, Mn 5 Si 3 metallic phase of manganese silicide has been found. The silicide phase has been found to grow on the irradiation. © 2009 Elsevier B.V. All rights reserved.