Study On The Structure And Magnetic Properties Of Bi³⁺ And Yb³⁺ Doped Cu-Co-Based Ferrites

Nano ferrite materials as ferrimagnetic materials are a special kind of magnetic oxides,based on their excellent physical and chemical properties,can be widely used in computer memory chips,transformer cores,ferromagnetic fluid,microwave absorption,magnetic resonance imaging,magnetic recording media,and other fields.In this paper,Cu-Co nano ferrites and Zn-Cu-Co nano ferrites were synthesized by the sol-gel method.The effects of the pH value of precursor solution and metal cation doping on the structure and magnetic properties of ferrites were investigated.This paper mainly includes the following three works:1.Bi³⁺doped Cu_0.2Co_0.8Fe_2-xBi_xO₄（x=0.0,0.025,0.05,0.075,0.1）nano ferrites were synthesized by the sol-gel method.X-ray diffraction（XRD）analysis showed that the sample was a spinel structure.The lattice constants of Bi³⁺doped samples increase with the increase of Bi³⁺doping,the lattice constants of the Bi³⁺doped samples were larger than that of the pure Cu-Co nano ferrite.The average crystallite size of the Bi³⁺doped samples decreased from 108.32 nm to 67.81 nm,and the decrease in dislocation line density indicated that the crystallinity of the samples was improved.Fourier transform infrared spectroscopy（FT-IR）reveals the absorption band and its specific location within a certain range and verified the spinel structure of the sample again.In addition,with the increase of Bi³⁺doping,the absorption band moves to the high-frequency direction.Scanning electron microscopy（SEM）revealed that the samples were spherical and cubic shapes.The elements contained in the sample were characterized by energy dispersive X-ray spectroscopy（EDX）,which proved that Bi³⁺was successfully doped into Cu-Co nano ferrite.The vibrating sample magnetometer（VSM）analyzes the magnetic properties of the sample.The results showed that the residual magnetization and coercivity of the samples decreased with the increase of Bi³⁺doping.However,due to the superexchange effect,the saturation magnetization increases first and then decreases with increasing of Bi³⁺content.When the content of Bi³⁺is 0.025,the sample has high saturation magnetization and coercivity,and the magnetic properties of the sample are the best.2.The pH value of the precursor solution was changed during the synthesis of Cu_0.2Co_0.8Fe₂O₄nano ferrite samples by sol-gel method,and the influence of the solution on the microstructure and magnetic properties of Cu_0.2Co_0.8Fe₂O₄nano ferrite was studied.XRD analysis showed that all the synthesized samples had spinel phase structures.According to Scherrer’s formula,the average crystallite size of the sample is between 60 nm and 68 nm,which indicates that pH value has a certain influence on it.The cation distribution proved that the ionic spacing of samples synthesized at different pH values was different.The characteristic absorption peaks belonging to the spinel structure can be seen from FT-IR spectra,which verifies the spinel structure of the synthesized sample again.The absorption peak also shifted with the change in pH value,indicating that different pH values caused the redistribution of cations in the sample.The SEM image shows that the samples are all cubic,and there is a certain degree of agglomeration due to magnetic properties.Elemental analysis shows that the sample has a pure phase structure and no other impurity phase.It can be seen from the hysteresis loop of the sample that the sample has ferromagnetism.When pH=10,the magnetic parameters of the synthesized samples are the maximum,such as saturation magnetization,residual magnetization,and coercivity.The samples can be used in the field of magnetic recording.Therefore,the magnetic properties of Cu-Co nano ferrites are relatively good at pH=10,and the research on Cu-Co nano ferrites can be deepened on this basis.3.Yb³⁺doped Zn-Cu-Co nano ferrites were synthesized by sol-gel method with chemical formula Zn_0.1Cu_0.2Co_0.7Fe_2-xYb_xO₄（0≤x≤0.1;in steps of 0.025）.X-ray diffraction（XRD）shows that the sample is a cubic spinel structure,and the impurity phase YbFeO₃appeared when the doping amount x≥0.075.Fourier infrared transform（FT-IR）revealed the information of chemical bonds and functional groups of the sample,and two characteristic absorption peaks were found near 390 cm^-1and 590 cm^-1,which were consistent with the structure of spinel.The morphologies of ferrite samples are spherical and cubic and polycrystalline structures are observed by transmission electron microscopy and selective electron diffraction.The energy dispersion spectrum reveals the elements and components of the sample,including Zn,Cu,Co,Fe,O,and Yb,without other impurity elements.The magnetic properties of the samples were analyzed by the hysteresis loop.The coercivity first decreased and then increased with the increase of doping amount,showing a soft magnetic behavior.When x=0.05,the highest saturation magnetization was obtained,which was 65 emu/g.The squareness of the sample is low.According to the differential plot of the hysteresis loop,it can be judged that the sample has the properties of the single domain and multi-domain.Thus,Yb³⁺doped Zn-Cu-Co ferrites provide a valuable research direction for the preparation of communication and high-frequency components.