ABSTRACT
With a view to investigate the elastic behavior of Nd(0.67)A(0.33)MnO(3) (where A=Ca, Sr, Ba, Pb) manganite system, the samples were prepared by the sol gel method. After characterizing the samples structurally, a systematic investigation of ultrasonic longitudinal and transverse sound velocities of all the samples was undertaken by pulse transmission technique in the temperature range, 100-300K. It has been found that all the elasticity parameters, including Debye temperature, are found to increase continuously with increasing ionic radii of the dopant ion. All the samples are also found to exhibit anomalies in both the longitudinal and transverse velocities near their ferro to para magnetic transition (T(C)) temperatures. Apart from this, Nd(0.67)Ca(0.33)MnO(3) sample is also found to exhibit, a transition at its charge ordering temperature (T(co)). An explanation for the observed elastic anomalies based on a mean field theory has been given.
ABSTRACT
Materials with the compositional formula La(0.67-x)Bi(x)Sr(0.33)MnO(3) (where x = 0, 0.1, 0.2, 0.3) prepared by a citrate gel route were used with a view to investigating the elastic behaviour of manganites in the vicinity of their T(C). The structural characterization of the materials clearly indicates that all the samples have a rhombohedral structure with [Formula: see text] space group. The magnetic (T(C)) as well as the metal-insulator (T(P)) transition temperatures determined by AC susceptibility and resistivity measurements, respectively, are found to decrease continuously with increasing bismuth concentration. Finally, the ultrasonic longitudinal velocities of all the samples are found to exhibit considerable softening in the vicinity of their magnetic transition temperatures, and an effort has been made to explain the observed behaviour by mean field theory and the Jahn-Teller phenomenon.
