Investigation Of Chemical States, Electrical And Magnetic Properties Of Sr₃Co₂Fe₂₄O₄₁ Hexaferrite

C02Z type hexaferrite Sr3Co2Fe24〇4i has good sotf magnetic properties, such as highpermeability, high resonance frequency，high thermal stability and low loss. It has potentialapplications in many high-frequency microwave devices. In recent years，large low-fieldmagnetoelectric effect at room temperature was also observed in Sr3Co2Fe24〇4i. Hence, itbecame a hot mateiral in the reaseach areas such as magnetoelectric sensors, low-power logicdevices and information storage devices. However, few reports has been seen on thechemical states, AC electric properties and doping vario-properties of Sr3Co2Fe24041.On theother hand, the rapid development of integrated electronics need the device components tobe miniaturized. Therefore, two-dimensional thin film mateirals are more required in theelectric devices. However, no reports have been seen on the Sr3Co2Fe24〇4i films.In order to solve the above problems, the chemical states，DC and AC electricalproperties of Sr3Co2Fe24〇4i and the magnetic properties of Sr3Co2Fe24〇4i with different ionsubstitutions has been studied in this thesis. Furthermore, the preparation techniques andmagnetic propeties of the Sr3Co2Fe2404i thin film have also been investigated.The detailed research contents and results are listed as follows:Firstly，Chemical states of SnCo2Fe2404i are investigated. The results show that bothFe3+and Fe2+ions are present.The presence of Fe2+is due to the appearance of oxygenvacancies in high heat sintering process. The emergence of Fe2+affects the valence of cobaltions+. As a result, part of Co2are oxidized to Co3+. The chemical states of the magnetic ionsin Sr3Co2Fe2404i are similar to those of the spinel structure materials with similar ingredients.Secondly, DC and AC electric properties of Sr3Co2Fe24〇4i are investigated. The DCresults show that the conduction mechanism of Sr3Co2Fe24〇4i is a typical semiconductor character. The resistivity at300K is3.8*108Q.cm? the activation energy is0.53eV. Theimpendance modulus plots show a non-Debye type of relaxation in the mateiral. Theactivation energy calculated from temperature-dependent impendance modulus is0.74eV.Thirdly，the effects of Ba2+and Zn2+substitution on the microstaictures of Sr3Co2Fe2404iare systematically investigated. The effects of Ba2+and Zn2+substitution on magneticproperties of Sr3Co2Fe2404i at different temperatures are also studied. The results indicatethat all the Z-type hexaferrites with Ba2+or Zn2+substitutions can be obtained at propersintering temperatures. As the Ba2+proportion increases, the saturation magnetization ofdopped Z-type hexaferrite tends to decrease generally, but coercive field exhibites no distinctvariation tendencies. As the Zn2+proportion increases, the saturation magnetization ofdopped Z-type hexaferrite tends to increase firstly and then decrease. No distinct vairationtrend is also observed in the coercive field. On the other hand，as temperature decreases, thedopped Z-type hexaferrites exhibite good soft magnetic properties and no magnetic phasetransitions are observed with changing the temperature. Moreever, the saturationmagnetization increases with the temperature.Finally, the preparation techniques and magnetic propeties of the Sr3Co2Fe24〇4i thinfilm are investigated.The results show that film is epitaxially grown with an interlayerbetween the film and the substrate. The high resolution TEM results show that the Z type"T" block in the Sr3Co2Fe24〇4i film is not formed. The prepared film is probably a strainedM-phase film. The magnetic properties results show that the coercive fields of the film aremuch larger than the bulk Sr3Co2Fe24〇4i，but much smaller than the reported results of pureM-phase film. Therefore, we inferred that the prepared film is possibly a Co doped M-phasefilm.