Spin structure in exchange-biased epitaxial ferromagnetic oxide bilayers

We investigate the spin structure of exchange-biased ferromagnetic bilayers for varying thicknesses near the critical thickness of the biasing layer. The epitaxial La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO)/ SrRuO$_{3}$ (SRO) ferromagnetic oxide bilayers were grown on (001) SrTiO$_{3}$ single-crystal substrates by pulsed laser deposition with atomic-layer control. We find a $\sim $2Ênm critical thickness of the biasing layer for the disappearance of exchange bias. The antiferromagnetic interfacial exchange permits manipulation of the frozen-in spin structure, and the ferromagnetism of each layer enables direct magnetization measurements. From these measurements, we infer the thickness dependence of the spin structure of the biasing layer in terms of domain walls perpendicular and parallel to the bilayer interface. We find that parallel domain walls can be frozen into the biasing layer for thicknesses near the critical thickness.