Ferromagnetic Resonance and Spin Transport in Epitaxial Manganite/Ruthenate Bilayers

Spin current generation by spin-pumping from a ferromagnet into a non-magnetic metal has been of great interest recently. However the role of the interface in the efficient pumping of spin current into the non-magnetic metal has not been addressed extensively. We address this issue by studying coherent interfaces in epitaxial oxide bilayers. Here we report recent results on spin pumping in pulsed-laser deposited bilayers of the ferromagnetic metal La_2/3Sr_1/3MnO₃ (LSMO) and the paramagnetic metals SrRuO₃ (SRO) and CaRuO₃ (CRO). X-ray diffraction indicates excellent crystallinity of the bilayers. CRO layers are under tensile strain on LSMO films grown on LSAT substrates, in contrast to SRO layers which are under compressive strain. Ferromagnetic resonance measurements of LSMO films indicate that the Gilbert damping parameter can be as low as 1×10^-3. This damping increases with the addition of an epitaxial ruthenate overlayer of SRO or CRO consistent with spin pumping. From the ruthenate thickness dependence of the Gilbert damping, we estimate that the spin diffusion length is larger in CRO than in SRO. We will also discuss the role of proximity-induced magnetism on spin transport in bilayers with SRO versus CRO, which has no ferromagnetic transition.