Chemical synthesis of Nd _<i>x</i> Co _{1− <i>x</i>} Fe ₂ O ₄ hybrid nanoparticles for permanent magnet applications: structural, magnetic and electrical properties

Nd-doped CoFe₂O₄ spinel ferrites were synthesized <i>via</i> the sol-gel method, confirming a cubic spinel structure. Increasing Nd concentration expanded the lattice parameter (8.3900-8.4231 Å) and unit cell volume while reducing grain size. FT-IR analysis validated the spinel phase. Nd doping enhanced the dielectric constant by affecting space charge polarization and charge hopping, with conductivity following a Debye-type relaxation mechanism. Cole-Cole plots indicated grain boundary effects and polaron hopping conduction. Magnetic properties improved with Nd³⁺ content, with <i>M</i> _s and <i>H</i> _c reaching 5.621 emu g^-1 and 143.43 Oe at 4% doping. A transition from an antiferromagnetic to a ferromagnetic state was observed, with a high Curie temperature (<i>T</i> _m) of 292 °C, confirming a stable ferromagnetic phase. These findings highlight Nd-doped CoFe₂O₄ as a promising candidate for permanent magnet applications.