Enriching Magneto-Optical Functionalities in Iron Garnet Films via Compensation-Driven Magnetic Tuning

Magneto-optical functional devices based on iron garnet films are important for optical communication and integrated photonics, where Faraday rotation magnitude, sign, and spectral response can be tuned on demand. However, most reported compensation-related magneto-optical responses have been demonstrated in isolated compositions or different formulations, leaving it unclear how a single compositional variable can design compensation temperature, magnetic reversal, and telecommunication-wavelength Faraday response in a Bi-rich rare-earth garnet film. Here, a Bi-Eu-Ho-Ga iron garnet thin-film platform is established, in which magnetic compensation is systematically tuned through Ga-mediated Fe-sublattice dilution. By adjusting Ga content, compensation temperatures of 77, 187 K, 29, and 431 K are achieved in the same materials family. Consequently, distinct Faraday responses are realized at 300 K, including changes in rotation magnitude, sign, and spectra, where large Faraday rotation (-0.081 deg µm^-1) is achieved under a low saturation field (≈527 Oe), and a self-biased state with full zero-field rotation retention and a large reverse nucleation field (≈350 Oe) is realized. Temperature-dependent Faraday spectroscopy reveals systematic evolution of the magneto-optical transition energy associated with the compensation state. This work provides a composition-guided route to compensation-regulated Faraday responses in Bi-rich Eu/Ho co-substituted iron garnet films for telecommunication-wavelength components.