Tuning the Magnon Transport Properties of Y₃Fe₅O₁₂ with a Cobalt Phthalocyanine Molecular Layer

Transporting spin information using magnon currents in magnetic insulators has garnered considerable interest as a means to advance information technology. A material's magnon transport properties can be tuned indirectly by modifying the magnetic properties, on which the former heavily depend. Molecular functionalization, in which organic molecules form a hybrid interface with a substrate material, has been shown to be a promising approach to modify the magnetic properties of metallic materials. In this work, we go beyond metals and demonstrate that the interfacial interaction between the organic molecule cobalt phthalocyanine (CoPc) and the magnetic insulator Y3Fe5O12 (YIG) modifies the magnetic properties of YIG, thereby allowing us to tune the transport properties of magnon currents in this magnetic insulator. Comparing a device with a YIG/CoPc interface to a simple YIG device, we find that the functionalized device exhibits larger amplitudes of nonlocal signals for both electrically and thermally excited magnon currents. Through the measurement of field-dependent nonlocal magnon signals and ferromagnetic resonance (FMR) in the YIG/CoPc device, we observe that the interfacial effect changes the magnetic anisotropy of the YIG, resulting in a larger saturation field. Moreover, the device with the CoPc overlayer exhibits a larger electrically excited magnon diffusion length at low temperatures due to the reduced Gilbert damping constant, as verified by FMR measurements. Our findings give us insight into the potential use of molecular functionalization to enhance magnon transport in magnetic insulators through the interfacial hybridization effect.