Structural and magneto-transport properties of LCMO–STO composites

Abstract

A manganite matrix-based composite series, (1 − x)La_0.67Ca_0.33MnO₃(LCMO) − (x)SrTiO₃ (STO), has been prepared by the solid state route. Influence of STO phase on structural and magneto-transport properties of LCMO phase has been investigated. By X-ray diffraction, scanning electron microscopy, and Fourier transform of infrared spectroscopy, we find that there is no interdiffusion between the LCMO and STO phases. Measurements of resistivity on these samples reveal that the parent sample shows a distinct metal–insulator (M–I) transition of intrinsic type at a temperature close to the Curie temperature, whereas composite samples show two possible transitions, intrinsic as well as extrinsic. The series exhibits a conduction threshold at x = x _m ∼ 20%, up to which extrinsic M–I transition temperature decreases along with an increase in extrinsic magnetoresistance; whereas, above x _m these trends of variation are reversed.

Keywords:

• CMR-based composites
• grain boundaries
• extrinsic and intrinsic MR
• M–I transition

Acknowledgements

The authors acknowledge the members of Central Instrumentation Facility Lab, Birla Institute of Technology, Mesra for providing SEM and FT-IR facilities. The authors also acknowledge Dr R. Rawat, UGC-DAE Consortium for Scientific Research, Indore Centre, India, for providing MR facility. S. Keshri is grateful for the financial assistance from the Department of Science and Technology (DST), India. L. Joshi and S. S. Rajput are grateful to the Council of Scientific and Industrial Research and DST, India, for providing fellowship.