Enhancement of spin-charge current interconversion by oxidation of rhenium

•An oxidation of rhenium enhances charge-spin interconversion compared with the pure rhenium state.•THz time domain spectroscopy is used to demonstrate the inverse charge-spin conversion via a magnon excitation.•The mechanism of the enhancement is not explained simply by the resistivity increase originating from the oxidation, and the optical phonon scattering in the rhenium oxide.