Biomedical subjects

T Saha-Dasgupta

Publications and source records attributed to T Saha-Dasgupta.

6 recordsLinked to original sources

PubMed2006

Origin of ferromagnetism and its pressure and doping dependence in Tl2Mn2O7.

Using the Nth order muffin-tin obital downfolding technique, we investigate the origin of ferromagnetism in pyrochlore Tl2Mn2O7. It is found to be driven by a hybridization induced spin polarization of delocalized charge carriers derived from Tl-s and O-p states. The mean-field estimate of the ferromagnetic transition temperature Tc estimated using computed exchange integrals are found to be in good agreement with measurements. We find an enhancement of Tc for moderate doping with nonmagnetic Sb and a suppression of Tc upon application of pressure, both in agreement with experimental findings.

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PubMed2005

Na2V3O7: a frustrated nanotubular system with spin-1/2 diamond ring geometry.

Following the recent discussion on the puzzling nature of the interactions in the nanotubular system Na(2)V(3)O(7), we present a detailed ab initio microscopic analysis of its electronic and magnetic properties. By means of a nontrivial downfolding study we propose an effective model in terms of tubes of nine-site rings with the geometry of a spin-diamond necklace with frustrated inter-ring interactions. We show that this model provides a quantitative account of the observed magnetic behavior.

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PubMed2004

Does the self-trapped magnetic polaron exist in electron-doped manganites?

We show from ab initio density-functional calculations and model studies that, in the electron-doped manganite LaxCa1-xMnO3 (x<<1), unbound electrons are introduced into the conduction band, which then trap themselves in the exchange-induced magnetic potential wells forming the self-trapped magnetic polarons (STMP). Hopping beyond the nearest neighbors drastically reduces the binding energy, while the Jahn-Teller coupling increases it somewhat, resulting in a net binding of about 100+/-20 meV. The electron is self-trapped in a seven-site ferromagnetic region, beyond which the lattice is essentially antiferromagnetic. In light of the recent experiments of Neumeier and Cohn, our results suggest that the STMP may be present in the lightly electron-doped manganites.

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PubMed2001

Band-structure trend in hole-doped cuprates and correlation with T(c max).

By calculation and analysis of the bare conduction bands in a large number of hole-doped high-temperature superconductors, we have identified the range of the intralayer hopping as the essential, material-dependent parameter. It is controlled by the energy of the axial orbital, a hybrid between Cu 4s, apical-oxygen 2p(z), and farther orbitals. Materials with higher T(c max) have larger hopping ranges and axial orbitals more localized in the CuO2 layers.

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PubMed2001

Modeling the electronic behavior of gamma-LiV2O5: a microscopic study.

We determine the electronic structure of the one-dimensional spin- 1 / 2 Heisenberg compound gamma-LiV2O5, which has two inequivalent vanadium ions, V(1) and V(2), via density-functional calculations. We find a relative V(1)-V(2) charge ordering of roughly 70:30. We discuss the influence of the charge ordering on the electronic structure and the magnetic behavior. We give estimates of the basic hopping matrix elements and compare with the most studied (alpha)'-NaV2O5.

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PubMed2000

Electronic structure of Sr2FeMoO6

We have analyzed the unusual electronic structure of Sr2FeMoO6 combining ab initio and model Hamiltonian approaches. Our results indicate that there are strong enhancements of the intra-atomic exchange strength at the Mo site as well as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss the possibility of a negative effective Coulomb correlation strength ( U(eff)) at the Mo site due to these renormalized interaction strengths.

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