Influence of Neodymium Doping on the Thermomagnetic Response and Colloidal Behavior of Copper Ferrite Nanoparticles

In this work, CuNdxFe2-xO4 (x = 0.00 - 0.11) nanoparticles were synthesized via a sol-gel autocombustion method and systematically investigated to evaluate the impact of neodymium substitution on their structural, magnetic, and heating performance for magnetic hyperthermia applications. X-ray diffraction confirmed the formation of spinel structures across all compositions. Magnetic characterization revealed a non-monotonic trend in saturation magnetization (Ms), reaching a maximum value of 62.11 emu/g at x = 0.05, while coercivity (Hc) varied between 236 and 273 Oe, reflecting the influence of Nd3+ on magnetic anisotropy. The magnetocrystalline anisotropy constant (K) was evaluated using both coercivity-based and high-field approaches, confirming enhanced anisotropy at moderate Nd substitution. Corresponding Néel relaxation times (τN) ranged from ~5 to 22 ns, supporting efficient magnetic heating for selected compositions. Zeta potential measurements demonstrated enhanced colloidal stability with moderate Nd substitution, with values exceeding +30 mV, suggesting favorable dispersion conditions for biomedical use. Magnetic hyperthermia performance was assessed under an alternating magnetic field (23.8 kA/m, 357 kHz) using both Box–Lucas and Newton Cooling models. The highest specific absorption rate (SAR) values, were observed for x = 0.03, 0.05, and 0.11. These findings underscore the importance of optimizing rare-earth substitution to modulate surface charge, magnetic anisotropy, and relaxation behavior.