Carrier density change in Colossal Magnetoresistive Pyrochlore Tl2Mn2O7

摘要

Hall resistivity and magneto-thermopower have been measured for colossalmagnetoresistive Tl2Mn2O7 over wide temperature and magnetic-field ranges.These measurements revealed that a small number of free electron-like carriersis responsible for the magneto-transport properties. In contrast to perovskiteCMR materials, the anomalous Hall coefficient is negligible even in theferromagnetic state due to negligibly small skew scattering. The characteristicfeature in Tl2Mn2O7 is that the carrier density changes with temperature andthe magnetic field. The carrier density increases around TC as the temperatureis lowered or as the magnetic field is increased, which explains the CMR ofthis material. The conduction-band-edge shift, which is caused by the strongs-d interaction between localized Mn moments and s-like conduction electrons,is a possible mechanism for the carrier density change.