Investigation of magnetic transitions through ultrasonic measurements in double-layered CMR manganite La_(1.2)Sr_(1.8)Mn_2O_7

摘要

A polycrystalline, double-layered, colossal magnetoresistive manganite La_(1.2)Sr_(1.8)Mn_2O_7 is synthesized by sol-gel process and its magnetic and ultrasonic properties were investigated in the temperature range 80-300 K. The sample has Curie temperature at 124 K, where the sample exhibits a transition from paramagnetic insulator to ferromagnetic metallic state. The longitudinal sound velocity measurements show a significant hardening of sound velocity below T_C, which may be attributed to the coupling between ferromagnetic spins and longitudinal acoustic phonons. The magnetization and ultrasonic studies reveal the presence of secondary transition at ≈ 260 K in this sample. The present sound velocity measurement results confirm the reliability of ultrasonic investigations as an independent tool to probe magnetic transitions in manganites.