Electronic phase separation in LaMnO3+δ-layers:: Usable as a tunneling barrier?

Thin LaMnO3+delta-layers were prepared by DC-magnetron sputtering. The structural, magnetic and electronic properties can be tailored by varying the preparation parameters. By reducing the oxygen excess delta within LaMnO3+delta, the lattice constant as well as the activation energy enlarges representing the semiconducting behavior. Beneath a reduced magnetic moment, the LaMnO3+delta-layers seem to show spinglass behavior and an exchange bias field with decreasing delta. This exchange bias is attributed to an exchange interaction between ferromagnetic clusters and the antiferromagnetic matrix. The different areas might be due to electronic phase separation. In order to realize full-oxide, all-manganite tunneling junctions, it was attempted to prepare high-quality LaMnO3+delta/La0.7Ca0.3MnO3-multilayers, which showed indeed a high quality of stacking with smooth interfaces and without significant Ca diffusion. Tunneling experiments with LaMnO3+delta-barriers and Au and Ir electrodes were successfully performed at low temperatures. Tunneling was observed up to barrier thicknesses of 20 nm and junction areas of around 0.02 mm(2). The result could be explained in that respect that the ferromagnetic clusters might represent localized states required for inelastic multi-step tunneling.