First-principles Calculations of Complex Crystalline Compounds

Datum

16.04.2012

Zeit

15:30 - 16:30

Sprecher

Soumyajit Sarkar

Zugehörigkeit

S N Bose National Centre for Basic Sciences, Kolkata/India

Sprache

en

Hauptthema

Materialien

Andere Themen

Materialien, Physik

Host

Grit Rötzer

Beschreibung

We have studied microscopic origin of many exciting and intriguing physical properties of different spinel compounds, based on density functional calculations. we propose a possible orbital ordering in MnV2O4 which consists of orbital chains running along crystallographic a and b directions with orbitals rotated alternatively by about 45 degree within each chain. Our study shows that the correlation-driven orbital ordering has a strong influence on the structural transitions in this system. The proposed orbital arrangement favors a noncollinear magnetic ordering of V spins, as observed experimentally. Our calculations provide a microscopic understanding of the origin of the insulating behavior of another spinel compound FeCr2S4, which turn out to be driven by Coulomb enhanced spin-orbit coupling operative within the Fe-d manifold. We also investigate the possible role of the structural distortions in this particular compound. Our study unravels the microscopic origin of different behavior of two very similar spinel compounds FeCr2S4 and FeSc2S4. This contrasting behavior is driven by the differences in hybridization of Fe d states with Cr/Sc d states and S p states in the two cases. This leads to important differences in the nature of the magnetic exchanges as well as the nearest-versus next-nearest neighbor exchange parameter ratios, resulting into significant frustration effects in FeSc2S4 which are absent in FeCr2S4. Low temperature insulating phase of CuIr2S4 has been studied and it has been shown that the insulating picture is mainly due to orbitally driven Peierls like transition. we have also investigated orbital ordering in FeV2O4, a spinel with orbital degrees of freedom both at Fe and V sites. .

Letztmalig verändert: 16.04.2012, 09:35:12