Electronic interactions between graphene and cobaltite thin film La0.7Sr0.3CoO3 and its magnetic consequences

Abstract

We have successfully synthesized and transferred graphene (Gr) monolayers on top of epitaxial mixed valence La0.7Sr0.3CoO3 (LSCO) thin films. Raman spectroscopy reveals that Jahn-Teller (JT) modes associated with the oxygen octahedral distortions usually unobserved for bare LSCO are activated by the deposited graphene. The appearance of these JT modes in the Gr/LSCO heterostructure is attributed to the electronic interactions at the interface between the graphene and the LSCO thin film promoting intermediate spin states of the Co ions. As a result, the magnetic properties of LSCO are affected. Indeed, magnetization measurements show a phase transition at ~135 K which is due to the presence of the graphene while the ferromagnetic transition of bare LSCO films is observed at~200 K. This magnetic phase is confirmed by Raman spectroscopy measurements as a function of temperature revealing a vibrational transition around the same temperature.