| MnxZn1-xCu0.2Fe1.8O4 (x=0.1, 0.2, 0.3, 0.4, 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 200℃,300℃,400℃,500℃,600℃for 4 h 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 MnxZn1-xCu0.2Fe1.8O4 (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9) samples annealed below and at 500℃are single-phase spinel structure. But, the sample annealed at 600℃exist muchα-Fe2O3. The particle sizes of samples with different Mn content are estimated from the X-ray spectra to be 20-35 nm, as measured by scanning electron microscope (SEM). The results of vibrating sample magnetometer (VSM) indicate that the saturation magnetizations (MS) of all MnxZn1-xCu0.2Fe1.8O4 (x=0.1, 0.2, 0.3, 0.4) samples are very small, so these samples aren't fit for the technological applications. For the MnxZn1-xCu0.2Fe1.8O4 (x=0.5, 0.6, 0.7, 0.8, 0.9) unannealed samples and samples annealed at 500℃, the variation of saturation magnetization (MS) nonlinearly increase with increasing Mn content, and the samples (.x=0.8) have maximal saturation magnetization; In addition, the coercivities of samples steeply increase with increasing Mn content.The synthesized temperature of nanoparticles investigated by differential thermal analysis (DTA) is in the range of 170-190℃. X-ray photoelectron spectroscopy (XPS) shows that most of Mn exist in Mn3+ state before and after annealing, and Fe exist in Fe3+/2+ mixed states before annealing and in Fe3+ state after annealing。The decrease of content ratio of Fe and Mn in surface layer after annealing indicates that the annealing induces to the increase of Mn content in surface layer. The annealing leads to the increase of percentages of Mn and Fe in surface layer. The Mn and Fe oxides exist in surface layer, but the nanoparticles are still single-phase spinel structure. |
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