RHEED study on continuously repeated step flow and layer-by-layer growth modes in SrRuO3/SrMnO3 superlattice

Nanolayered superlattices composed of ferromagnetic SrRuO3 and antiferromagnetic SrMnO3 layers were grown on SrTiO3 (100) substrates by pulsed laser deposition. Multilayers were grown under predetermined synthesis conditions resulting in growth of SrRuO3 and SrMnO3 by step flow and layer-by-layer modes, respectively. The growth of SrMnO3 was observed to occur through the layer-by-layer during the entire deposition process despite the expected increase in surface roughness because of the incorporation of SrRuO3 upper layers. Monitoring by reflection high-energy electron diffraction (RHEED) revealed that the growth of every SrMnO3 layer consisted of a pre-stage during which the gaps on the relatively rough SrRuO3 surface were filled before the actual growth of the SrMnO3 layer, which resulted in incomplete half oscillation and change from spot patterns to streaky patterns. The in-plane lattice constant did not show any considerable change in the case of SrRuO3 and SrMnO3 layers, despite the considerable lattice mismatch between the two materials (SrRuO3, SrMnO3) and SrTiO3. On the other hand, the RHEED patterns showed the existence of lattice mismatch effects in the out-of-plane lattice constant, which showed significant strains of opposite signs in the different layers, indicating a strong dependence on the composition of the layers and superlattice periodicity. In this paper, the growth characteristics of a SrRuO3/SrMnO3 multilayer along with its magnetic properties will be discussed.