Influence of the cooperative Jahn-Teller effect on the transport- and magnetic properties of La_{7/8}Sr_{1/8}MnO_3 single crystals

摘要

The low-doped magnetic perovskite La_{7/8}Sr_{1/8}MnO_3 undergoes within theparamagnetic-semiconducting phase a first-order structural transition due toantiferrodistorsive ordering of Jahn-Teller deformed MnO_6 octahedra. Thisallows to study not only the influence of the spin configuration on themagneto-transport properties (CMR effect) but also the role of orbital orderand disorder. The orbital ordering transition (at 269 K in zero magnetic field)causes a doubling of the resistivity (regardless of the CMR effect in appliedmagnetic fields) and a drop of the paramagnetic susceptibility. The lattermight be interpreted in terms of a shrinking of spin polarons. Externalmagnetic fields shift the ordering transition to lower temperatures accordingto the field-induced decrease of the carrier localization. The magnetic field -temperature phase boundary line was investigated by means of magnetoresistance(up to 12 T) and pulsed-fields magnetization measurements up to 50 T. Thepronounced magnetization anomalies, associated with the phase transition,vanish for fields exceeding 20 T. This behaviour has been attributed to afield-induced crossover from antiferrodistorsive order to anondistorsive/ferromagnetic orbital configuration.