Paramagnetic phase in single-crystalLaMnO3

Abstract

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 $T_{\mathrm{JT}}$ in a single crystal of the single-valent compound ${\mathrm{LaMnO}}_3.$ A positive Weiss constant increases discontinuously on raising the temperature through $T_{\mathrm{JT}},$ but the Curie constant remains unchanged. Above $T_{\mathrm{JT}},$ a nearly temperature-independent resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ and thermoelectric power $\alpha \mathrm{}\left(T\right)\mathrm{}$ that, unlike below $T_{\mathrm{JT}},$ are insensitive to the oxidation state of the ${\mathrm{MnO}}_3$ array are suggestive of charge transport by vibronic charge carriers.