Ferroelectric substrate effects on the magnetism, magnetotransport, and electroresistance of La0.7Ca0.3MnO3thin films on BaTiO3

Abstract

La${}_{0.7}$Ca${}_{0.3}$MnO${}_{3}$ optimally doped epitaxial films were grown on ferroelectric BaTiO${}_{3}$ substrates. Electronic transport (magnetoresistance and electroresistance) and magnetic properties showed important anomalies in the temperature interval between 60 and 150 K, below the metal-insulator transition. Scanning probe microscopy revealed changes in BaTiO${}_{3}$ surface morphology at those temperatures. La${}_{0.7}$Ca${}_{0.3}$MnO${}_{3}$ thickness is a critical factor: 120-\AA{}-thick films showed large anomalies sensitive to electric poling of the BaTiO${}_{3}$, whereas the behavior of 150-\AA{}-thick films is closer to that of the reference La${}_{0.7}$Ca${}_{0.3}$MnO${}_{3}$ samples grown on SrTiO${}_{3}$. We propose that, through inhomogenous strain and electric polarization effects, the ferroelectric substrate induces an inhomogenous spin distribution in the magnetic layer. This would imply the coexistence of in-plane and out-of-plane ferromagnetic patches in La${}_{0.7}$Ca${}_{0.3}$MnO${}_{3}$, possibly interspersed with antiferromagnetic regions, as it has recently been theoretically predicted. Substrate poling effects are investigated, and a magnetoelectric coupling is demonstrated.