Effect of dysprosium substitution on magnetic and structural properties of NiFe_2O_4 nanoparticles

This work investigated the effect of dysprosium (Dy) ions on the structural, microstructural and magnetic properties of nickel nanospinelferrite, NiFe₂O₄. The nanoparticles (NPs) of NiDy_xFe_2–xO₄ (0.0 ≤ x ≤ 0.1) were prepared via the hydrothermal method. The formation of cubic phase of Ni nanoferrite was confirmed through X-ray diffraction, field emission scanning and transmission electron microscopy. Moreover, the magnetic properties of NiDy_xFe_2–xO₄ (0.01 ≤ x ≤ 0.10) NPs were discussed. The magnetization versus field, M(H) curves exhibit super paramagnetic nature at room temperature and ferrimagnetic nature at low temperature (10 K). A noticeable improvement in the different deduced magnetic parameters is obtained especially for the NiDy_0.07Fe_1.93O₄(x = 0.07) product. The obtained result is mostly derived from the substitution of Fe³⁺ ions of smaller ionic radii with Dy³⁺ ions of larger ionic radii that will strengthen the super exchange interactions among nanoparticles. The calculated squareness ratios are found to be much less than 0.5, due to the effect of spin disorder in the surface regions of NiDy_xFe_2–xO₄ (0.01 ≤ x ≤ 0.10) NPs. The Dy³⁺ ions substitution increases the magnetic hardness (higher values of remanence M_r, coercivity H_c, and magnetic moment n_B) of nickel nanoferrite samples.