Frustration and Grace Under Pressure: Three Tales about Novel Oxides
CIC nanoGUNE Seminars
- Speaker
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John Mitchell, Argonne Natinal Lab, Argonne, USA
- When
-
2010/09/15
14:00 - Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
- Add to calendar
- iCal
Complex oxides provide an exceptionally powerful vehicle for understanding a
wide range of electronic and magnetic phenomena in condensed matter science.
Here I discuss some recent results in which control of material synthesis or
crystal growth at ambient or high pressure yields new insights in magnetic
frustration, oxide conductors, and multiferroicity.
• The field of geometric frustration of magnetism has been widely studied
using pyrochlore systems, calling for new materials and topologies. The
RBaCo4O7 (R=Y, Tb-Lu, Ca) system is one such new topology, formed by an
alternative stacking of the alternating Kagome and triangular layers found in
pyrochlores. We have explored the chemistry, structure and magnetic properties
of the Y member, demonstrating the extreme sensitivity of magnetic frustration
to oxygen content. Magnetic diffuse scattering on single crystals reveal a
microsopic, qualitative picture of the spin organization in this frustrated
magnet.
• Negative thermal expansion material orthorhombic Sc2W3O12, a white,
insulating powder, transforms into a new phase, a black, metallic compound,
under high P, T conditions. The crystal structure of the recovered phase
Sc2/3WO4 was determined from synchrotron x-ray powder diffraction data.
Sc2/3WO4, is a paramagnetic metal with a dense, monoclinic structure
containing 1-D chains of edge-sharing WO6 octahedra. Sc2/3WO4 is unusual among
conducting oxides, as there is little evidence of thermal activation or
lattice involvement. Rather, Sc2/3WO4 bears resemblance to doped amorphous
semiconductors.
• Recent density functional theory calculations have predicted that the
family of compounds MTiO3 (M = Mn, Fe, Ni) are promising candidates where a
polar lattice distortion can induce weak ferromagnetism. We have prepared the
corresponding Fe member at high pressure. It shows a sharp antiferromagnetic
(AF) transition at as well clear evidence of ferroelectricity. Importantly, we
have shown the existence of weak ferromagnetism, validating the ‘materials
by design’ approach in this multiferroic.
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