Abstract
Abstract In order to examine the existence of different phase transitions, the ultrasonic longitudinal modulus (L) and its first (ΔL/ΔT) and second (Δ2 L/Δ2 T) differentials have been established for two different perovskite manganites over a wide range of temperatures, La0.67Sr0.33MnO3 from 460 to 300 K and Nd0.67Sr0.33MnO3 300 to 150 K. The anomalies in L and its differentials at T C (≈378 K) in La0.67Sr0.33MnO3 are due to the ferromagnetic metal transition; the changes at T C (≈234 K), T CO (≈194 K) in Nd0.67Sr0.33MnO3 represent the ferromagnetic transition and charge ordering transition respectively. The existing phase transitions are due to a strong electron-phonon interaction arising from the Jahn-Teller effect and spin-phonon interaction from the linear magnetostriction effect. The first (ΔL/ΔT) and second (Δ2 L/Δ2 T) differentials of L are identified as an effective approach for the clear identification/detection of different phase transitions in the above systems over a wide range of temperatures.
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