Elastic properties of double layered manganites R1.2Sr1.8Mn2O7 (R = La, Pr, Nd, Sm)

The polycrystalline colossal magnetoresistive double-layered manganite samples R1.2Sr1.8Mn2O7 (R = La, Pr, Nd, Sm) were prepared by the sol-gel method and their room temperature elastic behavior was investigated by ultrasonic pulse transmission technique at 1 MHz. The values of elastic constants were calculated from longitudinal and shear velocities and they were corrected to zero porosity using Hasselman and Fulrath's formulae. The elastic constants of the samples were also estimated by Modi's heterogeneous metal-mixture rule which is based on the metal ions present in the samples. The measured, corrected, and estimated values of elastic moduli are found to increase with decreasing rare earth ion size. The variation of elastic moduli with the size of the rare earth ion is interpreted in terms of strength of interatomic bonding.