Sound velocity anomaly at around X ≈ 1/8 in La1-xCaxMnO3

The sound velocity v(s)(T) of La1-xCaxMnO3 (0.08 less than or equal to X less than or equal to 0.30) has been measured and two types of v(s)(T) anomalies have been observed. One is the v(s)(T) minimum around the ferromagnetic transition temperature T-c, and the other is the v(s)(T) upturn below the characteristic temperature T* which is lower than T-c. T*, as a function of the Ca concentration X, shows a maximum at about X = 1/8 and may be related to the onset of the charge-ordered phase similar to the v(s)(T) anomalies in La1-xSrxMnO3.