Spin dynamics in La_0.67Sr_0.33MnO3/YBa₂Cu₃O_7-δ heterostructures

Spin polarization in superconductors has largely been studied via injection of spin-polarized electrical currents, with relatively little attention paid to spin currents generated via spin wave excitations. To this end, we have fabricated heterostructures of the cuprate superconductor yttrium barium copper oxide (YBCO) with the half-metallic ferromagnet lanthanum strontium manganite (LSMO) via pulsed laser deposition on (LaAlO₃)_0.3(Sr₂TaAlO₆)_0.7 (001) substrates. In this study, we fix the LSMO thickness at 30 nm and vary the YBCO thickness from 2-17 nm. We have verified that the YBCO superconducts with T_c varying from 55-88 K depending on YBCO thickness (with a minimum thickness of 5 nm required for superconductivity). To characterize spin wave transport, we perform ferromagnetic resonance (FMR) as a function of temperature and YBCO thickness. We find that the resonance linewidth of bare LSMO increases with decreasing temperature, which is attributed to increased two-magnon scattering at lower temperatures. Additionally, with the addition of 17 nm of YBCO, we see a near doubling of the FMR linewidth at all temperatures, indicative of spin pumping into the YBCO and possibly the coexistence of spin polarization with superconductivity.