Nanocrystalline Mn-doped Ni–Cu ferrites with a high cut-off frequency and initial permeability: Suitable for advanced electronic devices and biomedical applications

The microstructural and electromagnetic properties of Mn-doped Ni0.50-xMnxCu0.50Fe2O4 (x = 0.0, 0.10, 0.20, 0.30, 0.40) magnetic nanoparticles are studied. Compositions are produced by the combustion method, and samples prepared from these powders are sintered at different sintering temperatures. The Rietveld refinement of X-ray diffraction (XRD) data confirmed that all compositions have cubic spinel structures with an Fd-3m space group. The average crystallite size is within 8–65 nm measured by different methods. The porosity of the surface, average grain diameter, and grain distribution are measured using optical micrographs. The high cut-off frequency of 10 MHz is observed in the initial permeability as a function of frequency plots. The maximum Curie temperature of 855 K is found for the x = 0 sample. The maximum relative quality factor (2636) and lowest relative loss factor (0.04) are found for x = 0.4. The initial permeability as a function of frequency is also measured at liquid nitrogen temperature (77 K). The “law of approach to saturation (LAS)” is used for magnetization data and the highest saturation magnetization value 61 emu/g is obtained for x = 0.3. The "Jonscher universal power law" fitted the ac electrical conductivity with large dispersion at a higher frequency region and a small polaron hopping model is applicable in this case. The dielectric constant exhibit dispersive behavior at low frequency and follow Koop's as well as Maxwell-Wagner's two-layer models. At 100 Hz the maximum value of the dielectric constant is 2.8 × 105. Nyquist plot representation stated that the electrical conduction mechanism in these ferrites is mainly due to the influence of the grain and grain boundary effects. An electrical equivalent circuit is suggested to explain the impedance analysis. Electric modulus studies confirm the non-Debye type relaxation process of the compositions. Tuning all of the properties specifies that the synthesized magnetic nanoparticles may be an optimistic application for high-frequency electronic devices and biomedical applications.