Thermal variations of the Jahn-Teller effect in a CMR manganite La_(0.7)Ca_(0.3)MnO_3 and charge and magnetic ordering in ~(57)Fe doped rare earth manganite

摘要

Domain fluctuations at low temperature are evidenced in perovskite-type rare earth manganites by two local methods: X-ray absorption and Mossbauer spectroscopies. For the CMR compound La_(0.7)Ca_(0.3)MnO_3, the thermal variations of the prepeak at the O K-edge, obtained by XAS measurements, show that the large prepeak observed at 300 K becomes a double peak below 200 K. These shape changes are very smooth and gradual around T_c and indicate the existence of FMM domain fluctuations around the PMI-FMM transition temperature. For Sm_(0.5)Ca_(0.5)MnO_3 doped with 1.5% ~(57)Fe, the Mossbauer spectra evidence charge and magnetic ordering phenomena below T_(co) ≈ 270 K. The magnetic transition, spread on a large temperature domain, is attributed to fluctuations in the antiferromagnetic state.