Interplay of Spins, Orbitals, Charges, and Lattice Instabilities in Complex Oxides
- Datum: 18.02.2016
- Uhrzeit: 14:00
- Vortragender: Prof. Martin Jansen
- Max Planck Institute for Solid State Research, Stuttgart, Germany
- Ort: Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Saale)
- Raum: Seminarraum A.2.20
Multinary oxides constitute a remarkably versatile and prolific class of
materials. They have continued to play a major role in the fields of
high temperature superconductivity (HTSC) and colossal magneto
resistivity (CMR), or, more recently, of multiferroics and spintronics.
Although a lot of effort has gone into unraveling the phenomena of HTSC
in cuprates and of CMR in manganates, no fully consistent and conclusive
microscopic explanation has become available yet. In the first place,
this unpleasant state is due to the high complexity of the problems
resulting among others from strong electron correlation, and coupled
charge, spin and orbital ordering in collective systems. Moreover,
virtually all oxide materials showing HTSC or CMR include severe
structural disorder, even decay into multiphase systems (phase
separation, stripe formation), a fact that has impaired theoretical
analyses commonly relying upon translational invariance, and has blurred
Against this background, it would be highly desirable to employ fully periodic and chemically well-defined materials as model systems for studying charge, spin and orbital ordering, either coupled or independent. We have tried to tackle this issue by providing new families of structurally and compositionally well-defined oxide based functional materials displaying
- Frustrated magnetic exchange interactions and orbital ordering on trigonal lattices in silver nickelates.
- Wigner crystallization vs. charge density waves in quasi one dimensional, mixed valent cuprates and manganates.
- Lattice instabilities and competing spin structures in 3d-5d double perovskites.
Besides full characterizations with respect to structures, physical
properties and electronic structure analyses, particular emphasis has
been given to aspects of solid state synthesis. In order to achieve well
defined valence states and structural perfection, special, in part
newly developed, synthesis protocols, e.g. the "azide/nitrate route",
needed to be employed.