Spin-pumping experiments in superconductor–ferromagnet heterostructures, which probe spin-sinking by the superconductor, have revealed a variety of complex behaviors. Most experimental studies have focused on conventional $s$-wave superconductors combined with metallic or insulating ferromagnets. Here, we study a $d$-wave superconductor paired with a half-metallic ferromagnet in epitaxial $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{7-\delta }/\mathrm{L}{\mathrm{a}}_{0.7}\mathrm{S}{\mathrm{r}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ heterostructures with two crystalline orientations: one in which YBCO is $c$-axis oriented and the other in which YBCO grows along the (103) direction. Using ferromagnetic resonance (FMR), we probe the temperature-dependent Gilbert damping coefficient α. For (103) heterostructures, α(T) initially decreases below $T_c$, but then increases at lower temperatures, eventually exceeding normal-state levels. This behavior can be understood in terms of the opening of the superconducting gap and spin transport via nodal quasiparticles, whose contribution is enhanced when the $\mathit{ab}$ plane of YBCO is exposed at the interface. In stark contrast, $c$-axis heterostructures exhibit a pronounced enhancement of α(T) below $T_{\mathrm{C}}$, peaking at $\sim 0.65-0.7T_{\mathrm{C}}$ before decaying. This anomaly suggests the dominance of interfacial Andreev bound states, arising from a locally suppressed superconducting order parameter because of proximity effects with the half-metallic LSMO.

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• Spintronics
• Superconductivity
• Complex oxides
• Cuprates
• Manganites
• Electron microscopy
• Ferromagnetic resonance