Transport and magnetic anomalies due to A-site ionic size mismatch in La$_{0.5}$Ca$_{0.5-x}$Ba_{x}MnO$_3$

TL;DR

This study investigates how A-site ionic size mismatch influences electrical and magnetic properties in La$_{0.5}$Ca$_{0.5-x}$Ba$_{x}$MnO$_3$, revealing non-monotonic transitions from insulating to metallic states with notable magnetoresistance.

Contribution

It provides new insights into the role of ionic size mismatch in tuning the magnetic and transport properties of manganites, highlighting the evolution of phases with Ba substitution.

Findings

Non-monotonic variation of Curie temperature with Ba content

Intermediate x=0.1 shows ferromagnetic insulating behavior with thermal hysteresis

High magnetoresistance observed below Curie temperatures

Abstract

We present results of electrical resistivity, magnetoresistance and ac and dc magnetic susceptibility on polycrystalline samples of the type La(0.5)Ca(0.5-x)Ba(x)MnO(3) synthesized under identical heat treatment conditions. The substitution of larger Ba ions for Ca results in a non- monotonic variation of the curie temperature as the system evolves from a charge ordered insulating state for x=0 to a ferromagnetic metallic state for x=0.5. An intermediate compositino, x=0.1, interestingly exhibits ferromagnetic. insulating behaviour with thermal hysteresis in ac chi around the curie tem- perature (120K). The x=0.2 and 0.3 compounds exhibit semiconducting like behavior as the temperature is lowered below 300K, with a broad peak in rho around 80-100K: These compositions exhibit a weak increase in rho as the temperature lowered below 30K, indicative of electron localization effects. These compositions also undergo ferromagnetic transitions below about 200 and 235K respectively, though these are non-hysteretic; above all, for these compositions, MR is large and conveniently measurable over the entire tempera- ture range of measurement below Tc. This experimental finding may be of interest from the application point of view. We infer that the A-site ionic-size mismatch plays a crucial role in the deciding these properties.