| DATE: |
2014-10-08 13:30 - 14:30 |
| PLACE: |
RCAST, The University of Tokyo (main), #1 on the 2nd floor of 4-go-kan (TV conf.) |
| TITLE: |
IMSS Seminar 14-07 Spin wave dispersion in the helical spin ordered system SrFeO3 and CaFeO3 |
| CONTACT: |
Hironori Nakao 6025 |
| SPEAKER: |
Prof. Clemens Ulrich (The University of New South Wales, Australia) |
| ABSTRACT: |
In the ferrates SrFeO3 and CaFeO3, spin and charge degrees of freedom play
an intriguing role. Their detailed interplay results in various electronic
and magnetic phases, for example as consequence of charge order. The
ferrates are isoelectric to the Jahn-Teller distorted manganite system and
exhibit also colossal magnetoresistance effects. But in contrast, the
ferrates show a helical instead of a collinear spin structure. Oxygen
doping has a dramatic effect on the electronic properties of the ferrates
since the oxygen deficiencies order systematically, leading to different
well defined crystallographic phase with different electronic properties,
e.g. metal-insulator transitions or charge order. Remarkably, our elastic
and inelastic neutron scattering experiments have revealed an almost
universal magnetic behavior for all the different electronic phases. The
spin wave dispersion is comprising upward- and downward-dispersing branches
in the form of an hour glass. Such a dispersion is common to compounds with
metallic and charge-ordered insulating ground states and closely resembles
the extensively studied, universal dispersion of spin excitations in
layered copper oxides such has high temperature superconductors. The
helical spin arrangement is a consequence a competition between long range
double-exchange and short range superexchange interactions. Our
theoretical calculations were able to convincingly reproduce the helical
spin structure and the experimentally obtained spin wave dispersion in the
ferrates SrFeO3 and CaFeO3. |
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