Formation of magnetic polarons in lightly Ca doped LaCoO3

Abstract

We performed high field electron spin resonance, nuclear magnetic resonance and static magnetization measurements on a powder sample of lightly hole-doped La1-xCaxCoO3, x ∼ 0.002 in order to study the influence of the size of the substitution ion on the formation of the hole induced spin-state polaron. Previous works [1, 2] showed that doping of LaCoO3 with Sr in very small concentrations (x ∼ 0.002) yields the formation of a magnetic polaron with a big spin value and large spin orbital coupling. The Ca2+ ion, in contrast to the Sr2+ion, has almost the same ionic radius as the La3+ ion. Therefore, the substitution of Ca for La provides mainly a hole to the system without creation of a sizeable crystal field distortion around the substituted Ca ion. The data obtained on La0.998Ca0.002CoO3 provide experimental evidence that the introduced hole indeed plays the main role in the formation of the spin-state polaron. Accompanying crystal field distortions seem to play a minor role, e.g. influencing the fine splitting of the spin polaron energy levels and the contribution of the spin orbital coupling. © 2010 IOP Publishing Ltd.