Transport and Magnetic properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3: Effect of oxygen pressure, sample thickness and co-doping with Ca

Abstract

La0.7Ce0.3MnO3 is a relatively new addition in the family of colossal magnetoresistive manganites where the cerium ion is believed to be in the Ce4+ state. In this paper we report an extensive study the magnetotransport properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3 with variation in ambient oxygen pressure during growth and film thickness. We observe that the transport and magnetic properties of the film depend on the interplay between oxygen pressure, surface morphology, film thickness and epitaxial strain. The films were characterized by x-ray diffraction on a 4-circle x-ray goniometer. We observe an increase in the metal-insulator transition temperature with decreasing oxygen pressure. This is in direct contrast with the oxygen pressure dependence of La0.7Ca-0.3MnO-3 films suggesting the electron doped nature of the La0.7Ce0.3MnO3 system. With decreasing film thickness we observe an increase in the metal-insulator transition temperature. This is associated with a compression of the unit cell in the a-b plane due to epitaxial strain. When the system is co-doped with 50% Ca at the Ce site the system (La0.7Ca0.15Ce0.15MnO3) is driven into a insulating state suggesting that the electrons generated by Ce4+ is compensated by the holes generated by Ca2+ valence thus making the average valence at the rare-earth site 3+ as in the parent material LaMnO3.