Research On Adjusting Magnetic-dielectric Properties Of Co₂Z Ferrite By Rare Earth Elements

As wireless and high-frequency communication technologies rapidly develop towards miniaturization,integration,and high functionality,the demand for high-frequency antennas is increasing,particularly in terms of size reduction and high-frequency operation.These urgent requirements impose higher demands on ferrite/dielectric materials in the high-frequency range.Among them,Z-type hexagonal ferrite materials exhibit excellent performance in high-frequency soft magnetisms,especially Ba₃Co₂Fe₂₄O₄₁ ferrite material（referred to as Co₂Z ferrite）,which has become one of the main materials for high-frequency devices at present.Through performance regulation,it is expected that Co₂Z ferrite material can be used in high-frequency electronic devices,such as high-frequency inductors,high-frequency filters and antennas.This dissertation is devoted to investigating the aforementioned issues.Specifically,the study focuses on the Co₂Z hexagonal ferrite material and explores the use of rare earth element doping to control the material’s phase formation and microstructure,as well as to regulate its magnetic dielectric properties.The aim of this research is to produce high-quality materials that possess superior magnetic-dielectric properties.Based on these materials,the dissertation conducts design,simulation,and optimization research on microstrip patch antennas.The main points are as follows:Firstly,Ba₃Co₂Fe_24-xSm_xO₄₁（x=0.00,0.10,0.20,0.30,0.40,and 0.50）material was synthesized by substituting Fe³⁺ions in Co₂Z ferrite material with rare earth element Sm³⁺ions to modulate their properties.The materials were high-temperature sintered at 1225℃.After high-temperature sintering,the phase formation of the material remains unchanged while increasing the doping amount x of Sm³⁺ions from0.00 to 0.50.However,the lattice constant gradually increases and the measured density gradually decreases.This can be attributed to the incorporation of Sm³⁺ions,which causes a significant increase in the cell parameters and leads to the inhomogeneity of the lamellar structure of the material.In terms of magnetic properties,the doped Co₂Z ferrite retains good soft magnetic properties.The saturation magnetization intensity increases and then decreases,with a maximum value of Ms=45.03 emu/g（4πMs=2726.1 Gs）,and the permeabilityμ’shows a trend of increasing and then decreasing,with the material reaching a maximum value ofμ’=14.8 when x=0.30.Meanwhile,the dielectric constantε’shows a trend of increasing and then decreasing with the increase of Sm³⁺ions,when x=0.30,the dielectric constant of the material is around 17.1 in the 10 MHz-1 GHz band.Meanwhile,the materials were low-temperature sintered at 950℃ with 2.5wt%Bi₂O₃as a sintering aid.The XRD results showed the samples maintained a single hexagonal crystal phase.The grain size distribution analysis reveals that the average grain size of the material increased from2.53μm（x=0.0）to 7.81μm（x=0.5）with increasing Sm³⁺ion doping.In terms of magnetic properties,the saturation magnetization strength of the samples is maximum at x=0.30 with Ms=47.24 emu/g（4πMs=2910.4 Gs）,and in terms of permeability and dielectric constant,the real part of permeabilityμ’=8.4 and the real part of dielectric constantε’=14.1 at x=0.20.In conclusion,Sm³⁺ion substitution enhanced magnetic-dielectric properties by high-temperature sintering and low-temperature sintering of Sm³⁺ion-doped Co₂Z ferrite,and the mechanism of their influence was analyzed.Secondly,Ba₃Co₂Fe_24-xGd_xO₄（x=0.00,0.10,0.20,0.30,0.40,and 0.50）material was synthesized by substituting Fe³⁺ions in Co₂Z ferrite material with rare earth element Gd³⁺ions to modulate their properties.In this process,the pre-sintering temperature of the material was elevated in this process to further promote the synthesis of the material.The effect of Gd³⁺ions on the phase formation,microscopic morphology and magnetic dielectric properties of Co₂Z ferrite materials was investigated by high temperature sintering and low temperature sintering processes.After the high-temperature sintering process,Gd³⁺ions increase the lattice constant and promoted grain growth without changing the phase composition of the Co₂Z ferrite material.As the value of x increases from 0.00 to 0.20,the average grain size of the material increases from 2.44μm to 3.62μm.Meanwhile,the density of the material initially increases and then decreases with increasing Gd content.When x is 0.10,the material has a maximum density of 5.01 g/cm³.In terms of magnetic properties,when x is 0.15,the material has a saturation magnetization of Ms=48.01 emu/g（4πMs=3012.9Gs）and a coercivity of Hc=66.66 Oe.The magnetic permeability and dielectric constant of the material increase initially and then decrease with increasing Gd³⁺ion content.When x was 0.15,the material has a magnetic permeabilityμ’=13.6 and a dielectric constantε’=17.13,while also exhibiting low magnetic and dielectric losses.After low temperature sintering with the addition of a sintering aid,the material maintains a single ferrite phase and exhibits an increase in grain size from 2.2μm（x=0.00）to 3.5μm（x=0.20）,as well as a high material density.For the saturation magnetization strength and coercivity of the material,the relationship between magnetic anisotropy constant and coercivity was obtained through fitting of the initial magnetization curve.For the magnetic-dielectric properties,when x is 0.15,the real part of the magnetic permeabilityμ’is 12.2,and the real part of the dielectric constantε’is 17.61,which shows magnetic-dielectric properties of materials were enhanced.Thirdly,based on the application requirements of electronic device fabrication processes,Ba₃Co₂Fe_24-x（Sm Pr）_xO₄₁（x=0.00,0.02,0.04,0.06,0.08,0.10）material was synthesized by substituting Fe³⁺ions in Co₂Z ferrite material with Sm-Pr ions.Addition of 2.5wt%BBSZ（27wt%B₂O₃-35wt%Bi₂O₃-6wt%Si O₂-32wt%Zn O）glass powder was used to low-temperature sinter the material at 925°C and 950°C.Sm-Pr ion doping does not change the single-phase nature of the Co₂Z ferrite,but increases the lattice constant and affects the material density.The material exhibits the highest measured density at x=0.08.For the performance,the overall magnetic-dielectric characteristics of the samples sintered at 925℃ are lower than those sintered at 950℃.At 950℃,as x increases,the saturation magnetization Ms first increases from 40.6 emu/g（x=0.00）to45.91 emu/g（x=0.04）,then decreases to 34.02 emu/g（x=0.10）.The magnetic and dielectric spectra of the samples sintered at 950℃ shows that the real part of the magnetic permeabilityμ’reached a maximum of around 14.22（x=0.04）,and the real part of the dielectric constantε’reaches a maximum of around 12.77（x=0.10）.The experiment shows that the BBSZ sintering aid promoted the synthesis of the material,resulting in good compactness,high saturation magnetization,and good magnetic properties.Finally,based on the research of magnetic-dielectric materials in this dissertation,microstrip patch antennas were designed with a center frequency of 1 GHz（Antenna 1）and 2.5 GHz（Antenna 2）.After design,simulation,and optimization of the antenna parameters,the parameters of the two antennas were obtained:the width of Antenna 1（W_a）is 26.30 mm,the length（L_a）is 17.89 mm,and the bandwidth（B_W）is about 5.09%.The width of Antenna 2（W_a）is 10.58 mm,the length（L_a）is 7.20 mm,and the BW is about 5.31%.Both two antennas exhibit good radiation characteristics,verifying the application of magnetic-dielectric materials in miniaturized and high-performance microstrip patch antennas.