Abstract: Mn _x Zn _1-x Cu _0.2 Fe _1.8 O ₄(x=0.5, 0.6, 0.7, 0.8, 0.9) nanoparticles with spinel structure were synthesized by sol-gel auto-combustion method and annealed at 500℃ for 4h in air in order to study the structure and magnetic properties of Mn-Zn-Cu ferrite nanoparticles. The analysis of X-ray diffraction (XRD) shows that all samples are single-phase spinel structure. The particle sizes of samples with different Mn content are estimated from the X-ray spectra to be 30--40nm. X-ray photoelectron spectroscopy (XPS) shows that most of Mn exist in Mn ³⁺ state before and after annealing, and Fe exist in Fe ^3+/2+ mixed states before annealing and in Fe ³⁺ state after annealing. The annealing leads to the increase of percentages of Mn and Fe in surface layer. The results of vibrating sample magnetometer (VSM) indicate that the coercivities (H_C) of samples annealed at 500℃ steeply increase with increasing Mn content. The saturation magnetizations (M_S) of unannealed samples with increasing Mn content increase first and then decrease, and the samples (x=0.8) have maximal saturation magnetizations (M_S). The influence of annealing on the samples with different Mn content is different.

Key words: sol-gel auto-combustion, Mn-Zn-Cu ferrite, nanoparticles, annealing