Bi-doped rare-earth iron garnet films via lead-free liquid phase epitaxy: growth and magneto-optical properties

Abstract

High-quality bismuth-doped rare-earth iron garnet (Bi:RIG) single crystal films were grown on (GdCa)₃(GaMgZr)₅O₁₂ (SGGG) substrates via a lead-free liquid phase epitaxy (LPE) method. Bi₂O₃ was employed as both flux and dopant. The resulting films exhibit excellent crystallinity, featuring a pure garnet phase and a low lattice mismatch of 0.08% with the substrate. Micro-structure characterization reveals a dense and smooth surface morphology with well-defined interfaces. The prepared Bi:RIG films show exceptional optical transmittance in the 1100–1600 nm wavelength range, with peak transmittance exceeding 70% at the key optical communication wavelengths of 1310 nm and 1550 nm. Magneto-optical measurements yield Faraday rotation coefficients of 1341 deg. cm⁻¹ at 1310 nm and 838 deg. cm⁻¹ at 1550 nm. Furthermore, the material exhibits soft ferromagnetic behavior with a low saturation field of approximately 400 Oe, which is favorable for device miniaturization. This study demonstrates that eco-friendly LPE is a feasible approach for fabricating high-performance magneto-optical films for integrated photonic devices operating in the near-infrared region.