Rietveld Refinement, Cation Distribution, and Magnetic Properties of Gd ³⁺ ‐Substituted Co _0.5 Zn _0.5

Gadolinium‐substituted cobalt–zinc spinel ferrite nanoparticles, Co _0.5 Zn _0.5 Gd _x Fe _{2− x} O ₄ ( x  = 0.00–0.10), were synthesized by the sol–gel autocombustion method and calcined at 700 °C for 5 h. Rietveld refinement of X‐ray diffraction data confirmed a single‐phase cubic spinel structure (space group Fd 3¯m ) up to x  = 0.08. A secondary GdFeO ₃ phase appeared at x  = 0.10, indicating a Gd ³⁺ solubility limit between x  = 0.08 and 0.10. The lattice parameter increased overall from 8.3954(6) to 8.4159(7) Å, with a minor nonmonotonic deviation at low Gd content, due to substitution of larger Gd ³⁺ ions at octahedral B‐sites. Bertaut cation‐distribution analysis revealed progressive migration of Co ²⁺ ions from B‐sites to A‐sites with increasing Gd substitution. FTIR and SAED confirmed the formation of the spinel phase, while TEM showed agglomerated polycrystalline nanoparticles (13.5–25.5 nm), consistent with XRD results. Magnetic measurements indicated a decrease in saturation magnetization (45.73–33.01 emu g ⁻¹ ) and coercivity (392.9–199.1 Oe) with increasing Gd content due to B‐sublattice dilution, cation redistribution, and enhanced Yafet–Kittel spin canting. The ferrites exhibit promising soft magnetic characteristics and provide valuable insights into rare‐earth‐substituted spinel ferrites for future electromagnetic and functional material applications.