Abstract
The ultrasonic, magnetic and transport properties of Nd0:5Ca0:5Mn1xAlxO3 (x=0,0.03) were studied from 15 to 300 K. The temperature dependencies of resistivity and magnetization show that Nd0:5Ca0:5MnO3 undergoes a charge ordering transition at TCO 257 K. An obvious softening of the longitudinal sound velocity above TCO and a dramatic stiffening below TCO accompanied by an attenuation peak were observed. These features imply a strong electron-phonon interaction via the Jahn-Teller effect in the sample. Another broad attenuation peak was observed at around Tp 80 K. This anomaly is attributed to the phase separation between the antiferromagnetic (AFM) and paramagnetic (PM) phases and gives a direct evidence for spin-phonon coupling in the compound. For the x=0.03 sample, both the minimum of sound velocity and attenuation peaks shift to a lower temperature. The results indicate that the charge ordering and CE-type AFM state in Nd0:5Ca0:5MnO3 are both partially suppressed by replacing Mn with Al.
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