Effect of Er substitution on ultrasonic anomaly in Dy0.5−xErxBa0.5CoO3 cobaltates

Rare-earth cobaltates Dy0.5−xErxBa0.5CoO3 (x = 0, 0.03 and 0.05) have been systematically investigated to elucidate the effect of Er substitution on elastic as well as magnetic and transport properties. DC electrical resistance and AC susceptibility measurements showed that the x = 0 sample exhibited an insulating behavior and an anti-ferromagnetic (AFM) transition, TN at 198 K as well as ferromagnetic (FM) transition, TC at 260 K. Increasing of Er content suppressed the FM and AFM state suggestively due to the increase in size disorder arising from the size mismatch between A-site cations as shown from our calculation of variance σ2. On the other hand, both absolute longitudinal and shear velocities and related elastic moduli measured at 210 K decreased with Er content in conjunction with the declining in the FM domain indicating a weakening in elastic properties. A longitudinal velocity anomaly characterized by a drop in velocity upon cooling before hardening with further cooling was observed for all samples. This abnormal elastic anomaly can be attributed due to the Jahn–Teller (JT) distortion of intermediate-spin Co3+ ions. Analysis of the elastic anomaly using the mean-field theory suggested that it is related to the JT effect which transformed from dynamic to static type with decreasing temperature. The elastic anomaly shifted to lower temperature from 129 K (x = 0) to 124 K (x = 0.05) with Er substitution indicating a weakening of the static JT effect.

► Elastic properties of rare-earth cobaltates Dy0.5−xErxBa0.5CoO3 were studied.
► Elastic anomaly was observed around 124–129 K in the longitudinal mode.
► The anomaly was explained using mean-field theory and Jahn–Teller (JT) effect.
► Mean-field theory suggests transformation from dynamic to static JT effect.
► Elastic moduli at 210 K were found to decrease with decline in FM domain.