Influence of the cooperative Jahn - Teller effect on the transport - and magnetic properties of La 7 / 8 Sr 1 / 8 MnO 3 single crystals

Influence of the cooperative Jahn-Teller effect on the transport-and magnetic properties of La 7/8 Sr 1/8 MnO 3 single crystals Abstract The low-doped magnetic perovskite La 7/8 Sr 1/8 MnO 3 undergoes within the paramagnetic-semiconducting phase a first-order structural transition due to antiferrodistorsive ordering of Jahn-Teller deformed MnO 6 octahedra. This allows to study not only the influence of the spin configuration on the magneto-transport properties (CMR effect) but also the role of orbital order and disorder. The orbital ordering transition (at 269 K in zero magnetic field) causes a doubling of the resistivity (regardless of the CMR effect in applied magnetic fields) and a drop of the paramagnetic susceptibility. The latter might be interpreted in terms of a shrinking of spin polarons. External magnetic fields shift the ordering transition to lower temperatures according to the field-induced decrease of the carrier localization. The magnetic field-temperature phase boundary line was investigated by means of mag-netoresistance (up to 12 T) and pulsed-fields magnetization measurements up to 50 T. The pronounced magnetization anomalies, associated with the phase transition, vanish for fields exceeding 20 T. This behaviour has been attributed to a field-induced crossover from antiferrodistorsive order to a nondistorsive/ferromagnetic orbital configuration.