Transport and magnetic properties of laser ablated La_0.7Ce_0.3MnO₃ films on LaAlO₃

Abstract

La_0.7Ce_0.3MnO₃ is a relatively new addition to the family of colossal magnetoresistive manganites, in which the cerium ion is believed to be in the Ce⁴⁺ state. In this article, we report the magnetotransport properties of laser ablated La_0.7Ce_0.3MnO₃ films on LaAlO₃, and the effect of varying the ambient oxygen pressure during growth and the film thickness. We observe that the transport and magnetic properties of the film depend on the oxygen pressure, surface morphology, film thickness, and epitaxial strain. The films were characterized by x-ray diffraction using a four-circle goniometer. We observe an increase in the metal-insulator transition temperature with decreasing oxygen pressure. This is in direct contrast to the oxygen pressure dependence of La_0.7Ce_0.3MnO₃ films and suggests the electron doped nature of the La_0.7Ce_0.3MnO₃ 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. On codoping with 50% Ca at the Ce site, the system (La_0.7Ca_0.15Ce_0.15MnO₃) is driven into an insulating state suggesting that the electrons generated by Ce4+ are compensated by the holes generated by Ca²⁺, thus making the average valence at the rare-earth site 3+ as in the parent material LaMnO₃.