Photoacoustic effect at second-order phase transition in La1-xCaxMnO3

The gas-microphone photoacoustic (PA) technique has been applied to determine the second-order phase transition in manganite compounds La1-xCaxMnO3 (x - 0.1 and 0.2). A comparative analysis of the PA result with magnetization and electrical resistivity measurements has been performed. The doping of Ca causes the occurrence of ferromagnetic (FM) ordering. The FM transition temperature T-c, determined from magnetization loll Measurement, is 145 and 180 K for x = 0.1 and 0.2, respectively. The temperature at which the anomaly of PA signal occurs is consistent with T, determined from the magnetization measurement. The change of PA signal arises at the same temperature in both cases with decreasing and increasing temperatures, This implies that the paramagnetic to FM phase transition can be regarded as a second-order phase transition with no latent heat at T-c. (C) 2002 Elsevier Science B.V. All rights reserved.