Influence of Dy3+ Ions on the Microstructures and Magnetic, Electrical, and Microwave Properties of [Ni0.4Cu0.2Zn0.4](Fe2–xDyx)O4 (0.00 ≤ x ≤ 0.04) Spinel Ferrites

[Ni0.4Cu0.2Zn0.4](Fe2–xDyx)O4 spinel ferrite nanoparticles with different Dy3+ concentrations (0.00 ≤ x ≤ 0.04) were prepared by a citrate sol–gel auto-combustion technique. A strong correlation am...