Influence of superconducting proximity effect in LSMO/SIO Ferromagnetic Resonance*

Superconductivity and ferromagnetism are antagonistic phenomena: singlet-state Cooper pairs with antiparallel spins cannot survive in a ferromagnet. In some cases, triplet-state Cooper pairs, in which electrons have parallel spins, can be formed by proximity effect at ferromagnetic interfaces. We experimentally investigate ferromagnetic resonance (FMR) in trilayers consisting of a half-metallic La_0.7Sr_0.3MnO₃ and YBa₂Cu₃O₇ superconducting layers, with an interlayer of SrIrO₃, a high spin-orbit coupling material, which is expected to create a strong inhomogeneity of the magnetic field in momentum space. The FMR signal is studied as a function of temperature (10-150 K). It reveals a drastic change in the resonance signal when the YBa₂Cu₃O₇ becomes superconducting. This change will be discussed in terms of the formation of triplet Cooper, favored by the high spin-orbit coupling of SrIrO₃. The results will be discussed in the frame of the spin-pumping theory considering the superconductor a spin sink where part of the FMR generated angular momentum can relax.