Sol–Gel Synthesis and Multifunctional Characterization of Mo-Substituted YIG for High-Sensitivity Photodetection

We investigated the influence of molybdenum (Mo) doping on the structural, magnetic, electrical, and optoelectronic properties of yttrium iron garnet (YIG) synthesized via the sol–gel method. X–ray diffraction (XRD) with Rietveld refinement confirmed a single-phase garnet structure (x = 0–0.1), showing slight lattice expansion and crystallite growth due to oxygen vacancies and Fe²⁺ formation as charge-compensation mechanisms. Scanning electron microscopy reveals a morphology shift from dendritic networks (x = 0) to porous agglomerates (x ≥ 0.06). We observed a blue shift (~2–3 cm⁻¹) of Fe–O vibrational modes and mode splitting in the Raman spectra at high Mo levels, indicating local lattice distortion. ICP-OES verifies Mo incorporation close to nominal values. Magnetic measurements at 5 K reveal long-range ferrimagnetism, but saturation magnetization and Curie temperature (T_C ~545 K for undoped YIG) decrease with increasing Mo, consistent with Fe³⁺ → Mo⁵⁺ substitution and charge compensation. T_C aligns with models where Mo occupies mainly octahedral sites at low doping and both octahedral/tetrahedral sites at higher levels. Mo doping lowers room-temperature resistivity from ~10¹⁰ Ω to <8 × 10⁴ Ω (x = 0.1), showing n-type behavior with ~0.19 eV activation energy. Under 914 nm illumination, Mo-doped YIG exhibits a strong bolometric response (I_ph ~270 µA, responsivity ~2.16 × 10³ mAW^-1, D* ~10⁹ cm·Hz¹ᐟ²·W^-1), surpassing many oxide-based bolometric materials, highlighting its potential for advanced bolometers and spintronic devices.