| 1. |
- Balasubramanian, Padmanabhan, et al.
(author)
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Valence band electronic structure of Nd1-xYxMnO3 using X-ray absorption, photoemission and GGA plus U calculations
- 2013
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 189, s. 51-55
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Journal article (peer-reviewed)abstract
- The electronic structures of Nd1-xYxMnO3 (x=0-0.5) were studied using X-ray absorption near-edge structure (XANES) at the Mn L-3,L-2- and O K-edge along with valence-band photoemission spectroscopy (VB-PES). The systematic increase in white-line intensity of the Mn L-3,L-2-edge with doping, suggests a decrease in the occupancy of Mn 3d orbitals. The O K-edge XANES shows a depletion of unoccupied states above the Fermi energy. The changes in the O K-edge spectra due to doping reflects an increase in the Jahn-Teller distortion. The VB-PES shows broadening of the features associated with Mn 3d and O 2p hybridized states and the shift of these features to a slightly higher binding energy in agreement with our GGA + U calculations. The system shows a net shift of the occupied and unoccupied states away from the Fermi energy with doping. The shift in theoretical site-projected density of states of x=0.5 composition with respect to x=0 suggest a subtle change from a charge transfer to Mott-Hubbard type insulator. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Bhattacharjee, Satadeep, et al.
(author)
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Atomistic Spin Dynamic Method with both Damping and Moment of Inertia Effects Included from First Principles
- 2012
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:5, s. 057204-
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Journal article (peer-reviewed)abstract
- We consider spin dynamics for implementation in an atomistic framework and we address the feasibility of capturing processes in the femtosecond regime by inclusion of moment of inertia. In the spirit of an s-d-like interaction between the magnetization and electron spin, we derive a generalized equation of motion for the magnetization dynamics in the semiclassical limit, which is nonlocal in both space and time. Using this result we retain a generalized Landau-Lifshitz-Gilbert equation, also including the moment of inertia, and demonstrate how the exchange interaction, damping, and moment of inertia, all can be calculated from first principles.
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| 3. |
- Bhattacharjee, Satadeep, et al.
(author)
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Electronic structure of Co-phthalocyanine calculated by GGA plus U and hybrid functional methods
- 2010
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In: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 377:1-3, s. 96-99
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Journal article (peer-reviewed)abstract
- Electronic structure calculations have been performed for the Co-phthalocyanine molecule using density functional theory (DFT) within the framework of Generalized Gradient Approximation (GGA). The electronic correlation in Co 3d orbitals is treated in terms of the GGA+U method in the framework of the Hubbard model. We find that for U = 6 eV, the calculated structural parameters as well as the spectral features are in good agreement with the experimental findings. From our calculation both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are dominated by the pyrrole carbon, with a HOMO-LUMO gap of about 1.4 eV. The GGA+U results obtained with U = 6 eV compare reasonably well with the calculations performed using Gaussian basis set and hybrid functionals in terms of ground state geometry, spin state and spectral features. The calculated valence band photoemission spectrum is in quite good agreement with the recently published experimental results.
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| 4. |
- Bhattacharjee, Satadeep, et al.
(author)
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First principles calculations of magnetism, dielectric properties and spin-phonon coupling in double perovskite Bi2CoMnO6
- 2012
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:29, s. 295901-
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Journal article (peer-reviewed)abstract
- First principles electronic structure calculations have been performed for the double perovskite Bi2CoMnO6 in its non-centrosymmetric polar state using the generalized gradient approximation plus the Hubbard U approach. We find that the ferromagnetic state is more favored compared to the ferrimagnetic state with both Co and Mn in high spin states. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. The magnetic structure dependent phonon frequencies indicate the presence of a weak spin-phonon coupling. Using the Berry phase method, we obtain a spontaneous ferroelectric polarization of 5.88 mu C cm(-2), which is close to the experimental value observed for a similar compound, Bi2NiMnO6.
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| 5. |
- Bhattacharjee, Satadeep, et al.
(author)
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Theoretical Analysis of Inertia-like Switching in Magnets : Applications to a Synthetic Antiferromagnet
- 2012
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In: Physical Review X. - 2160-3308. ; 2:1, s. 011013-
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Journal article (peer-reviewed)abstract
- The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations. We observe switching phenomena on the time scale of tens of picoseconds, and inertia-like behavior in the magnetization dynamics. We explain the latter in terms of a dynamic redistribution of magnetic energy from the applied-field pulse to other possible energy terms, such as the exchange interaction and the magnetic anisotropy, without invoking concepts such as the inertia of an antiferro-magnetic vector. We also demonstrate that such dynamics can also be observed in a ferromagnetic material where the incident-field pulse pumps energy to the magnetic anisotropy.
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| 6. |
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| 7. |
- Choudhury, Debraj, et al.
(author)
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Tuning of dielectric properties and magnetism of SrTiO3 by site-specific doping of Mn
- 2011
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12, s. 125124-
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Journal article (peer-reviewed)abstract
- Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.
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| 8. |
- Haldar, Soumyajyoti, et al.
(author)
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Functionalization of edge reconstructed graphene nanoribbons by H and Fe : A density functional study
- 2012
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In: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 152:18, s. 1719-1724
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Journal article (peer-reviewed)abstract
- In this paper, we have studied functionalization of 5-7 edge-reconstructed graphene nanoribbons by ab initio density functional calculations. Our studies show that hydrogenation at the reconstructed edges is favorable in contrast to the case of unreconstructed 6-6 zigzag edges, in agreement with previous theoretical results. Thermodynamical calculations reveal the relative stability of single and dihydro-genated edges under different temperatures and chemical potential of hydrogen gas. From phonon calculations, we find that the lowest optical phonon modes are hardened due to 5-7 edge reconstruction compared to the 6-6 unreconstructed hydrogenated edges. Finally, edge functionalization by Fe atoms reveals a dimerized Fe chain structure along the edges. The magnetic exchange coupling across the edges varies between ferromagnetic and antiferromagnetic ones with the variation of the width of the nanoribbons.
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