Enhancement of spin mixing conductance in La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/LaNiO$_{3}$/SrRuO$_{3}$ heterostructures

We investigate spin pumping and the effective spin mixing conductance in heterostructures based on magnetic oxide trilayers composed of La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO), LaNiO$_3$ (LNO), and SrRuO$_3$ (SRO). The heterostructures serve as a model system for an estimation of the effective spin mixing conductance at the different interfaces. Our results show that by introducing a LNO interlayer between LSMO and SRO, the total effective spin mixing conductance increases due to the much more favourable interface of LSMO/LNO with respect to the LSMO/SRO interface. Neverheless, the spin current into the SRO does not decrease because of the spin diffusion length of $\lambda_\text{LNO}\approx$3.3 nm in the LNO. This value is two times higher than that of SRO. Our results show the potential of using oxide interfaces to tune the effective spin mixing conductance in heterostructures and to bring novel functionalities into spintronics by implementing complex oxides.