Ferromagnetic–paramagnetic transition temperature in bulk and nanostructured La_0.7Sr_xCa_0.3-xMnO₃（x=0.10, 0.15, and 0.20） manganite materials

Somasundaram Praveen Kumar^1,2，Kathiresan Sakthipandi¹，Ramamurthy Gayathiri¹，Mathu Sridhar Panday¹，Arumugam Karthik¹，Venkatachalam Rajendran¹

1. Centre for Nano Science and Technology, K.S. Rangasamy College of Technology, Anna University2. Research and Development Centre, Bharathiar University

摘 要：Series of bulk and nanostructured La_0.7Sr_xCa_0.3-xMnO₃（x = 0.10, 0.15, and 0.20） manganites were synthesized and characterized using different techniques. In the series, both the bulk and nanostructured La_0.7Sr_0.10Ca_0.20MnO₃ and La_0.7Sr_0.20Ca_0.10MnO₃ manganites have orthorhombic and rhombohedral structures, whereas La_0.7Sr_0.15Ca_0.15MnO₃ manganite has rhombohedral and orthorhombic structures, respectively. Online ultrasonic velocity and attenuation measurements were taken through an indigenously designed ultrasonic setup, and the analysis was done from 300 to 400 K during the aging of the samples to explore the structural/phase transitions. The bulk and nanocrystalline La_0.7Sr_xCa_0.3-xMnO₃ perovskite samples show the particle size distribution in the range of 197–943 and 24–93 nm, respectively. The addition of Sr²⁺ alters the size of particles, which decrease in size. The observed anomaly in ultrasonic velocities, attenuations, and elastic moduli is correlated with the ferromagnetic–paramagnetic（FM–PM） transition temperature（T_C） in both bulk and nanocrystalline perovskites. In addition, the shift in T_C and the magnitude and width of observed anomaly are correlated with the value of x to study the behavior of T_C.

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