Fyzikální ústav Akademie věd ČR

Seminar Wednesday, 12/03/2014 15:00 - 16:00

Speakers: Maria Valentyuk (I. Institute for Theoretical Physics, University of Hamburg, Germany; Department of Theoretical Physics and Applied Mathematics, Ural Federal University, Ekaterinburg, Russia)
Place: Na Slovance, main lecture hall
Presented in English
Organisers: Department of Condensed Matter Theory

Abstract: Essentially, the effects of magnetic frustration are provided by competing interactions between localized spins in the system. Such competition of exchange interactions brings a great diversity of unusual phenomena observed in magnetic materials. We were able to give a microcsopic description of magnetic interactions in following fascinating systems: a member of the multiferroic family,YMnO3, and an example of system with observed BEC of the magnons, BaCuSi₂O₆.
One of the well-known members of multiferroic family of rare-earth manganites is YMnO₃. Hexagonal modification of this crystal produces frustration of moments, localised on Mn atoms, leading to the magnetic degeneracy of the ground state. This effect complicates the understanding of ME effects in systems with nearly non-distorted triangular lattice. Recently synthesized stable orthorhombic phase of YMnO₃ also shows features that put complications in the determination of magnetic state and corresponding nature of FE displacements. Here, in the framework of ab-initio and low-energy model calculations the intrinsic mechanism of the observed effects is presented. We show that the account for spin-orbit coupling terms in spin models can give the correct description of magnetism and related effects in such materials.
Another revisited system with competing magnetic interaсtions is the low-dimensional magnet BaCuSi₂O₆. The new picture of interactions shows much better agreement with experiment and disproves existing speculations about BaCuSi₂O₆ as a frustrated magnet.