Magnetic exchange coupling in bilayers of two epitaxial ferromagnetic oxides

• Positive exchange bias in La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) bilayers on silicon.
• The cross-over from antiferromagnetic to ferromagnetic interface exchange coupling.
• Strong dependence on soft layer (LSMO) thickness.
• Could be due to interface domain walls, Zeeman, anisotropic and exchange energies.

Despite a decade of research effort on La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) bilayers (BLs), a full knowledge on the magnetic properties and integration of these BLs on silicon substrate is not yet in sight. In this paper, we report on the magnetic exchange coupling observed from the above two ferromagnetic oxide thin film BLs, prepared through a novel approach, called ‘domain matching epitaxy’. LSMO (100 nm)/SRO (45 nm) and LSMO (31 nm)/SRO (45 nm) bilayers have been epitaxially integrated with Si (1 0 0). Notably, in the former sample, positive exchange bias is observed – an indication of antiferromagnetic exchange coupling and is found to be absent in the latter. Furthermore, in the former sample, the cross-over from antiferromagnetic to ferromagnetic interface exchange coupling is noticed by varying the cooling field. We have verified that this coupling is of magnetic origin, not due to electrostatic interaction by inserting a thin (∼10 nm) SrTiO3 layer between LSMO and SRO. We believe that in addition to the formation of interface domain walls, the strong interplay among Zeeman, anisotropic and exchange energies could play a dominant role. Our results would have important implications for devices comprising of magnetic exchange coupled systems.