Structural and Magnetic Рroperties of Copper Substituted Mg-Ferrites

Polycrystalline ferrite powders of Mg1-xCuxFe2O4 (x = 0.2, 0.4, 0.6, 0.8, 1) system synthesized by ceramic technology have been investigated. Samples showed the non-monotonic dependency of heat generation effect in AC magnetic field with increasing concentration of copper. To reveal peculiarities of the structural and magnetic state of the samples and their influence on the heat generation ability we performed a complex study, including X-ray diffractometry, Mössbauer spectroscopy, Scanning electron microscopy, measurements of temperature dependencies of susceptibility and saturation magnetization, hysteresis parameters and FORC. Typical ferrimagnetic character with small coercivity and saturation magnetization was found. We carried out that anomalous influence of Cu2+ ion substitution respectively to the Mg1-xCuxFe2O4 ferrite powder manifested in heat generation ability rise up to x=0.6. The subsequent sharp reducing of this characteristic were accompanied by the main phase crystal structure distortion followed by phase separation to cubic and tetragonal structure. This was matched by in an increase of ferrite particles crystallite size and size distribution appearance. The saturation magnetization and Curie temperature dependencies observed for powders via Cu substitution was explained by phase composition, the cations distributions between ferrite sublattices, modulation of exchange interaction.

The Use of Kramers-Kronig Relations for Verification of Quality of Ferrite Magnetic Spectra

The complex initial permeability (CIP) as a function of frequency is one of the main properties of ferrites. This characteristic (CIP) is measured experimentally, therefore there can be found noisy, doubtful or incomplete parts of the spectrum. Thus there is a need for a method of evaluation of quality of CIP. In this article for evaluation of the quality of experimental CIP spectra of polycrystalline ferrite materials the KKR (Kramers-Kronig relations) are used. In order to apply KKR to experimentally measured data (i.e. data with finite limits) the method of transforming these integral relations into summation relations with finite limits is developed and described. This method can be used only for CIP given over the wide frequency rage, so that the imaginary part of CIP is fully presented. Using KKR with the help of CIP spectra model (based on the effects coming from polycrystal grain sizes and defects distribution) partly removes aforementioned limit. Thus with the help of the model we can also make CIP spectra reconstruction (in cases when CIP is noisy or incomplete) and CIP spectra decomposition.

Complex Permeability Spectra of Co-Substituted Lithium Zinc Perminvar Ferrite

The effect of Co-substitution on the complex permeability of LiZn ferrite was studied. The polycrystalline ferrite samples with a composition of ((Li0.5Fe0.5)0.8Zn0.2)1-xCoxFe2.05O4, where x varies from 0 to 0.08, were prepared by solid-reaction method. The sintered samples were annealed at 490oC for 96 h to produce perminvar effect. The complex permeability was measured in the frequency range from 1 MHz to 2 GHz. The Co-substitution can enhance the real part of complex permeability (μ’). The maximum μ’ appears when x=0.02. The Co-substituted LiZn samples, especially for x=0.02 and 0.04, present resonance-type magnetic spectra obviously. The μ’ of the sample for x=0.02 increases because the damping of domain wall movement decreases after the annealing treatment. The resonance character of the annealed sample becomes even more remarkable due to its domain wall stabilization.