Infrared absorption study of charge ordered $La{}_{0.5}Ca{}_{0.5-x}Sr_{x}MnO_{3}$ $(0.1\leq x\leq0.5$

Abstract

Infrared absorption study has been carried out on a series of half doped manganites, La 0.5 Ca 0.5−x Sr x M nO 3 (0.1 ≤ x ≤ 0.5), with varying magnetic ground state. The charge ordering transition observed in samples with x ≤ 0.3 is accompanied by a mode at ∼ 525cm −1 in addition to the stretching mode at 615cm −1 and bending mode at 400cm −1 . Phonon hardening is found to occur below the CE -type antiferromagnetic ordering temperature. The value of the insulating gap decreases on doping with Sr from 727cm −1 to 615cm −1 .