Paramagnetic phase in single-crystal LaMnO3

We report the observation of a peculiar conductive phase with ferromagnetic interactions and a Curie-Weiss paramagnetism above the cooperative Jahn-Teller orbital-ordering temperature T-JT in a single crystal of the single-valent compound LaMnO3. A positive Weiss constant increases discontinuously on raising the temperature through T-JT, but the Curie constant remains unchanged. Above T-JT, a nearly temperature-independent resistivity rho(T) and thermoelectric power alpha(T) that, unlike below T-JT, are insensitive to the oxidation state of the MnO3 array an suggestive of charge transport by vibronic charge carriers. [S0163-1829(99)51746-3].