Sintering-temperature effects on cation redistribution and magnetic response of the Y2.97Gd0.03Fe4.97La0.03O12 ceramic

In this work, we report a comprehensive investigation of the influence of sintering temperature (900, 1000, and 1100 °C) on the structural, morphological, and magnetic properties of the Y 2.97 Gd 0.03 Fe 4.97 La 0.03 O 12 garnet-type ceramic synthesized by the sol–gel method. Structural refinement confirms the predominance of the garnet phase in all samples and reveals a thermally induced emergence of a YFeO 3 secondary phase, quantified as 3.7 % at 1000 °C and 9.9 % at 1100 °C. Increasing the sintering temperature enhances crystallinity, increases the average crystallite size from 45 to 68 nm (≈51 %), and reduces the microstrain by ≈33 %. Infrared vibrational analysis shows red shifts in Fe–O stretching modes, indicating bond elongation and local lattice relaxation. Electron microscopy reveals grain growth and reduced porosity at 1000 °C, followed by abnormal coarsening and localized porosity at 1100 °C. Mössbauer spectroscopy demonstrates a temperature-dependent redistribution of Fe 3+ across octahedral and tetrahedral sublattices and confirms the persistence of Fe 2+ associated with oxygen-vacancy stabilization. This redistribution governs the magnetic response: the saturation magnetization increases from 15.37 emu g -1 (900 °C) to 18.46 emu g -1 at 1000 °C (≈20 %), then decreases to 15.27 emu g -1 at 1100 °C in parallel with the growth of the secondary phase. Remanent magnetization follows the same trend, whereas the remanent-to-saturation ratio remains nearly constant at ≈0.3, consistent with a multi-domain configuration. Coercivity decreases from 62 to 46 Oe (≈26 %), reflecting grain-size-assisted domain-wall motion. Collectively, these results show that sintering temperature provides a quantitative route to tune structural relaxation, cation redistribution, and magnetic behavior in this co-doped garnet system. The sample sintered at 1000 °C exhibits the most favorable combination of crystallinity, controlled porosity, and maximized magnetization, offering a mechanism-based framework for designing soft-magnetic and microwave-grade ceramics. • La–Gd co-doped YIG synthesized via sol–gel and sintered at 900-1100 °C. • Fe 3+ redistribution (a↔d) governs M s variation with temperature. • YFeO 3 fraction reduces M s beyond 1000 °C. • M s peaks at 1000 °C with reduced coercivity. • Structure-magnetism coupling enables tunable microwave ceramics.