Double exchange via t(2g) orbitals and the Jahn-Teller effect in ferromagnetic La0.7Sr0.3CoO3 probed by epitaxial strain.
The magnetic exchange in hole-doped ferromagnetic cobaltates is investigated by studying the magnetic and electronic properties of La0.7Sr0.3CoO3 films as a function of epitaxial strain. We found a strong-coupling double exchange mechanism between Co3+ (4t(2g)   2e(g)) and Co4+ (3t(2g)   2e(g)) high-spin states mediated by t(2g) electrons--in contrast to the moderate coupling provided by the e(g) exchange in manganites. The strong sensitivity of the Curie temperature TC to the bulk compression can be explained by the small bandwidth of the t(2g)-derived states. A strain-induced Jahn-Teller effect is likewise observed. The experimental results clarify the magnetic exchange mechanism in the cobaltates.
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany.
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D
Fuchs
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany.
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M
Merz
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany.
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P
Nagel
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany.
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R
Schneider
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany.
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S
Schuppler
Institut für Festkörperphysik, Karlsruher Institut für Technologie, 76021 Karlsruhe, Germany and Physikalisches Institut, Karlsruher Institut für Technologie, 76128 Karlsruhe, Germany.
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H
von Löhneysen