LAUSR

Abstract Dy3+ and Y3+ ions co-doped Zn0.5Mn0.5Fe2O4 (ZMDyYFe) (x=0.00-0.05) nanospinel ferrite nanoparticles (SFNPs) have been synthesized through an ultrasonication approach. The rare earth co-doping with Dy3+ and Y3+ ions was applied to tune the structural and magnetic properties of the ZnMn spinel ferrites. The influence of the co-doped of both Dy3+ and Y3+ ions on the structural, optical, and magnetic characteristics of Zn0.5Mn0.5Fe2O4 SFNPs was analyzed in detail by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high- resolution tunneling electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), and elemental mappings. XRD results revealed the formation of the spinel phases and the structural changes which were accompanied the Dy3+ and Y3+ ions co-doping. The cubic spinel phase of all samples has been confirmed by the application of Rietveld refinement. As the value of ``x`` increased up to x=0.04, the lattice constant was found to increase from 8.401 to 8.408 A and the size of the crystallites was calculated to be in the range 7.26 nm-11.10 nm. HR-SEM and HR-TEM micrographs also presented the cubic morphology of the products. Diffuse reflectance spectroscopy (DRS) measurements were done on pure and Dy3+ and Y3+ co-doped Mn0.5Zn0.5Fe2O4 SFNPs. Direct band gaps (Eg) were extracted from Tauc plots. Eg values existed in a narrow range between 1.64 eV and 1.74 eV. Magnetic investigations exhibited the superparamagnetic behavior at RT (room temperature) and ferrimagnetic behavior at 10 K for synthesized samples. At RT analyses, undoped Mn0.5Zn0.5Fe2O4 SFNPs had the maximum saturation magnetization (MS) of 34.84 emu/g and magneton number (nB) of 1.47 μB. An inverse proportion with the increasing ion ratio were observed among those parameters. The 10 K magnetization data revealed that co-doped Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs had magnetic parameters of MS,max= 67.39 emu/g, nB,max = 2.88 μB and HC,max = 574 Oe (HC: coercivity and max: maximum). Among the rest of the co-doped samples, MS and nB data had a similar negative trend with respect to the increasing ion ratio including the remnant magnetizations (Mr). The rest of the HC values were found to be between 275 Oe and 361 Oe. Squareness ratios (SQRs= Mr/MS) had a range of 0.181- 0.321 and confirmed the multi-domain wall structure for all SFNPs at 10 K. The maximum value of effective crystal anisotropy constant (Keff) 6.04 × 104 Erg/g belongs to Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs, and others have the same order of 104 Erg/g for Keff constants. Although this sample has the largest internal anisotropy field (Ha) of 1794 Oe, it can also be classified as a soft magnetic material like other nanoparticle samples. The Dy3+ and Y3+ ions co-doped ZMDyYFe (x=0.00-0.05) SFNPs, with varying structural and magnetic properties, can have potential applications in various areas such as magnetic switching, security, magnetic core, microwave absorption applications, nanofabrication and nanodevices.