Study On Preparation,Doping,Morphology,Structure And Magnetic Properties Of Magnetoplumbite Fe₂W Ferrites

The development of science and technology is inseparable from the development of new materials.As the basic material of electronic technology,magnetic material plays an important role in the development of science and technology in today's society.Ferrite as a member of the magnetic material family,after nearly half a century of development and improvement,has been widely used in various fields,such as aerospace,radar technology,ultra-high frequency microwave communication and other aspects.It can be divided into six types according to its crystal structure,among which M type and W type are the focus of current research.The magnetic properties of M-type ferrite have been improved by various means such as ion substitution,but it is close to the upper limit,The results of the study on W-type ferrite show promise.The research of Fe2W ferrite is still in the exploratory stage,and its various properties have not been fully utilized.Based on this,this paper focused on Fe2W type ferrite,prepared a series of samples related to it by solid phase method with nitrogen protection,and analyzed and studied a series of parameters such as sample preparation process,components,microstructure and magnetic properties.The main conclusions and innovative achievements are as follows:1.A series of W-type hexagonal ferrites with composition BaFe22+Fe,634+O27 at different temperatures was synthesized via a ceramic process in a reducing atmosphere during the whole process of calcination and sintering.The influence of temperature on the microstructure and magnetic properties is studied,the results are as follows:The samples of pre-sintering temperature between 1290 ??1330 ? are the pure phase of hexagonal crystal structure;The saturation magnetic polarization intensity(Js)is high and the coercivity(Hc)is low,showing the soft magnetic characteristics of W-type ferrite.The magnetic properties of testing magnets showed that the best pre,sintering temperature is]300 ?;X-ray photoelectron spectroscopy(XPS)has analyzed the element composition of Fe2 W ferrite and the existence of valence state of Fe.The spectrum shows that Fe mainly exists in the form of Fe(III),while there is a small amount of Fe(II).Therefore,it can be determined that part of Fe3+ can be converted into Fe2+ by the solid phase method protected by nitrogen,which also confirms the feasibility of the experiment.2.On the basis of controlling presintering temperature 1300 ?,W-type ferrite BaFe22+Fe16-x 3+O27(x=-0.8?-0.4?0·0?0.4?0.8 and 1.2)powders and magnets were prepared via the solid-state reaction in nitrogen.The influence of the iron content on the structure and magnetic properties is systematically studied.The main research results are as follows:all the samples without any extra impurity peak compared with standard w-type ferrite;The orientation of grain on grain axis varies with the content of iron.The value of crystal axis ratio c/a is almost constant,indicating that the symmetry of the crystal is hardly affected in the range of iron content change.The variation of sample remanence B,first increases and then decreases,which is consistent with the variation trend of saturated magnetization.Hcj and Hob of the sample magnet were consistent with the coercivity Hc of the magnetic powder.The quadrate ratio of the magnet is good,indicating that it is a typical permanent magnet.3.The influence of La substitution on the microstructure and magnetic properties of W type hexagonal ferrite was systematically studied by solid phase method with nitrogen protection.The main results are as follows:La substitution did not change the magnetoplumbite structure of W type ferrite,La3+ entered the magnetoplumbite crystal lattice,and the sample was the crystal structure of W type ferrite.The lattice constant a of the sample is basically unchanged,while the c value decreases with the increase of the amount of La3+doped.In addition,from the perspective of crystal axis ratio,it can be seen that the sample has a W-type structure.High saturation magnetization(MS)and low coercivity((Hc),soft magnetic characteristics of magnetic powder can be observed.With the increase of La substituent x,Ms first increased and then decreased,while Hc decreased with the increase of La substituent x.The magnetic anisotropic field Ha and the effective magnetic anisotropic constant Kefr decrease linearly with the increase of La substituent x.4.W-type ferrite Sr1-xLaxFe22+Fe163+O27(x=0.00,0.05,0.08,0.10.0.13 and 0.1 5)powders and magnets were prepared via the solid-state reaction in nitrogen.The main research results are as follows:all samples is only one magnetic lead phase,which means that La3+ lead into the magnetoplumbite lattice structure,did not form include them in the second phase,the method can get single type SrFe2W ferrite.With the increase of La3+ substitution,the morphology of the magnet remained basically unchanged.The saturation magnetization first increases and then decreases with the increase of substitution amount.The coercivity decreases with the increase of substitution.Studies on samples of magnets show that the trend of B,is consistent with that of Ms,and Hcj and Hcb of magnets have the same characteristics as Hc of magnetic powders.The samples are best able to make optical read-out of the magnetic storage information in erasable video and audio discs.5.W-type ferrite BaCoxFe2-x2+Fe163+O27(x=0.0-2.0)powders and magnets were prepared via the solid-state reaction with nitrogen protection.The main research results are as follows:Except for the sample x=1.5,all samples confirmed as single-phase W hexagonal structure,the space group is P63/MMC,no extra impurity peak.At x=1.5,a small amount of Ba2CO2Fe12O22 Y phase was detected as the second phase.Except for the sample x=1.5,the X-ray density and porosity of the sample increased with the increase of Co content,while the volume density decreased with the increase of Co content.The saturation magnetization Ms of magnetic powder first increased and then decreased,while the coercivity H,first decreased and then increased.The magnetic anisotropy and magnetic anisotropy fields decrease with the increase of Co content.Hcj and Hcb of magnets have the same characteristics as Hc of magnetic powders.For Co with the same content,the remanence Br of the magnet decreases with the increase of the measured temperature,the magnetic induction coercivity(Hcb)increases with the increase of the measured temperature.For the same temperature point,the remanent Br first increases and then decreases with the increase of Co content,Hcb decreased with the increase of Co content.In addition,Hcj\also shows a similar trend;The Hcj and Hcb of magnets have the same characteristics.6.The effect of the Co content replacing the Fe2+ in BaFe2W type ferrite BaCoxFe2-x2+Fe163+O27(x=0.0-0.8)on the magnetic properties was studied in detail.The main research results are as follows:all samples have only one magnetoplumbite phase,which means that Co2+enters the lattice of the magnetoplumbite.According to the results of Rietveld spectrum fitting,the experimental diffraction data of XRD is very consistent with the refined calculation value,which confirms the reliability and authenticity of the experiment.From the FT-IR spectra of the samples in the wave number range of 4000-400cm-1,the W-type hexagon ferrite structure was completely formed.The VSM test results show that at room temperature of 300K,the variation trend of saturation magnetization(Ms)first increases and then decreases with the increase of cobalt content,while the coercivity H,decreases with the increase of Co content.Interestingly,at a low temperature of 3K,the variation trend of saturation magnetization(Ms)first decreased and then increased with the increase of cobalt content,which was contrary to the change trend of Ms measured at room temperature,and Ms at a low temperature of 3K was higher than that at 300K.