Influence of rare earth ion substitutions on the structural, optical, transport, dielectric, and magnetic properties of superparamagnetic iron oxide nanoparticles

Superparamgnetic Fe 3 O 4 and RE:Fe 3 O 4 (RE = Dy, Nd, La) nanoparticles with an average crystallite size in the range of 15–24 nm, were synthesized by co-precipitation method. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), UV–Vis spectroscopy, LCR bridge, and two-probe technique. X-ray diffraction patterns of all the investigated samples reveal the typical phase of magnetite structure, with a small contribution of orthoferrite (NdFeO 3 ) as a secondary phase in Nd:Fe 3 O 4 sample. The saturation magnetization ( M s ) of the samples has values in the range from 41.8 to 52.3 emu/g, and decreases with RE ion doping depending on the ionic radius. Negligible values of the coercivity H c and remanence M r , indicate the superparamagnetic nature of the investigated samples. The calculated values of indirect optical band gap of Fe 3 O 4 and RE:Fe 3 O 4 nanoparticles are in the range of 0.9–1.25 eV. The dielectric constant of the samples decreases, while their activation energy increases with the increasing of ionic radii of dopants.