The results of studies of ferromagnetic resonance (FMR) of iridate/manganite epitaxial heterostructures in a wide range of microwave frequencies (1- 20 GHz) are presented. The magnitudes of imaginary and real parts of the spin mixing conductance of the heterostructure boundary determining the spin current were determined from the frequency dependence of the spin damping and changes in the resonance field of the FMR. It is shown that the value of the imaginary part of spin conductance is comparable to the real part, which may be caused by strong spin-orbit interaction occurring in 5d-oxides of transition metals (iridate). Keywords: ferromagnetic resonance, SrIrO3/La0.7Sr0.3MnO3 heterostructures, spin current, spin mixing conductance.

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We present results on experimental studies of spin current, measured under spin pumping at ferromagnetic resonance in wide frequency band 2-20 GHz for SrIrO3/La0.7Sr0.3MnO3 heterostructures fabricated by RF magnetron sputtering at high temperature. The epitaxial growth of the thin film in heterostructure by a cube-on-cube mechanism was confirmed by XRD and TEM analysis. Taking into account the contribution of anisotropic magnetoresistance the spin current was estimated as 1/3 of the total response. We show that both real and imaginary parts of spin mixing conductance are valuable for heterostructures with strong spin-orbit interaction in SrIrO3. Imaginary part of spin mixing conductance was estimated by means of shift of ferromagnetic resonance field of La0.7Sr0.3MnO3 layer in heterostructure. The spin magnetoresistance was evaluated from angular dependencies of magnetoresistance measured in planar Hall configuration. In order to extract the influence of anisotropic magnetoresistance a La0.7Sr0.3MnO3 film was measured as well. The spin Hall angle for heterostructure was found higher than for interface Pt/ La0.7Sr0.3MnO3.