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Abstract:
In the scientific description of unconventional transport properties of
oxides (spin-dependent transport, superconductivity etc.), the
spin-state degree of freedom plays a fundamental role. Because of this,
temperature-or magnetic field-induced spin-state transitions are in the
focus of solid-state physics. Cobaltites, e.g. LaCoO3, are prominent
examples showing these spin transitions. However, the microscopic nature
of the spontaneous spin crossover in LaCoO3 is still controversial. Here
we report magnetostriction measurements on LaCoO3 in magnetic fields up
to 70 T to study the sharp, field-induced transition at H-c approximate
to 60 T. Measurements of both longitudinal and transversal
magnetostriction allow us to separate magnetovolume and
magnetodistortive changes. We find a large increase in volume, but only
a very small increase in tetragonal distortion at H-c. The results,
supported by electronic energy calculations by the configuration
interaction cluster method, provide compelling evidence that above H-c
LaCoO3 adopts a correlated low spin/high spin state.
