Diffusion and segregation effects in doped manganite/titanate heterostructures

For the properties of devices based on oxide multilayers, interfaces play a crucial role. For ferromagnetic tunnel junctions the sign of the spin polarization depends on the barrier material and the interface termination. Here, we present a transmission electron microscopy study of heteroepitaxial trilayer systems consisting of a SrTiO3 insulating barrier sandwiched between La2/3D1/3MnO3 (D=Ca or Ba) electrodes grown on SrTiO3 substrates. Intermixing during growth depends on the earth alkaline ion: Ca segregates to the surface of the growing epitaxial thin film, leading to a Ca rich interface layer between the bottom electrode and the barrier. In contrast, no Ba segregation could be detected in the well lattice-matched Ba-doped film. In addition, a significant diffusion of both Ca and Ba into the SrTiO3 tunneling barrier is found, whereas the diffusion of Mn is negligibly small. Our results explain the different tunneling magnetoresistance in various manganite based tunnel junctions.