Bismuth-substituted lutetium iron garnet films with giant visible-range magneto-optical sensitivity

Magneto-optical materials are indispensable across modern physics, serving as the foundation for precision magnetic sensing, nonreciprocal photonics, and optical isolation technologies. The continual pursuit of materials with high Verdet constants has driven the development of garnet-based compounds exhibiting giant magneto-optical sensitivity. In this work, we report the growth and comprehensive magneto-optical characterization of bismuth-substituted lutetium iron garnet (LuBiIG), a material that combines the large spin–orbit coupling of bismuth with the lattice stability of lutetium iron garnet. LuBiIG films with thicknesses between 85 and 220 nm were grown by pulsed laser deposition and characterized at room temperature over the 500–820 nm wavelength range. The films exhibit an exceptionally high Verdet constant of up to −1.37×108 °m−1 T−1, peaking in the visible spectral range near 520 nm. These results position LuBiIG as a highly sensitive magneto-optical material suitable for advanced cryogenic detection and hybrid quantum applications.