Study Of Ion Substitution On The Property Modulation Of YIG Gyromagnetic Materials

Microwave ferrite devices such as microwave ferrite circulator and isolator play an important role in the transmitter/receiver components of microwave electronic systems.To adapt to the development trend of microwave electronic system integration miniaturization,reducing the size and volume of the ferrite device and improving the power withstand capability while guaranteeing the performance of the device is the developmental direction of the technology field.The yttrium iron garnet(Y₃Fe₅O₁₂,abbreviated as YIG)gyromagnetic ferrite material based on the device and has been widely used puts forward a high microwave permittivity and high spin-wave line width development requirements.Therefore,the study of the microwave dielectric constant of YIG and the regulation mechanism and method of the spin-wave linewidth is the key to improve the high microwave dielectric constant and power tolerance of such materials.In this dissertation,the microwave magnetic and dielectric properties of YIG are analyzed and optimized by means of ionic substitution and preparation process regulation.The mechanism of the macroscopic microwave dielectric properties of YIG affected by the nature of ionic bonding and the change of the electronic structure of the crystal is firstly investigated by the complex bond theory from the viewpoints of the crystal structure.The properties of ionic bonding,and the mechanism of the ionic substitution’s effect on the microwave permittivity and the dielectric loss of the YIG material is explained.The mechanism of ion substitution on the microwave dielectric constant and dielectric loss of YIG materials is explained,and it is verified by the results of the analysis of the electronic structure,magnetic ion valence changes and lattice vibration modes of the materials by means of first-principle calculations,XPS and Raman spectroscopy,etc.,which establishes the connection between the chemical bonding properties and microwave dielectric parameters of YIG,and puts forward an effective method to improve the microwave dielectric constant of YIG;at the same time,the use of the fast-relaxation ion substitution in combination with the control of the crystal grain size control,the mechanism and measures to improve the spin-wave linewidth of YIG are investigated on the basis of ensuring the low ferromagnetic resonance linewidth.The main conclusions of this dissertation are as follows:1.The effect of variation of crystal structure parameters on the intrinsic dielectric properties of the material was investigated.The chemical formula of YIG was split into binary bonding formulae,and important bonding property parameters such as ionicity,covalency,and crystal lattice energy of binary chemical bonding of YIG crystals with different ionic substitutions were calculated by using the complex bond theory.The crystal structural properties were correlated with the dielectric properties of the materials,and it was found that the combinations of the divalent Ca²⁺,Zn²⁺,Sr²⁺,and tetradentate Sn⁴⁺,Ti⁴⁺and so on Ion substitution helps to enhance the average ionicity of the binary bonding formula of YIG,because the ionicity of the material is directly proportional to the microwave dielectric constant;the improvement of ionicity increases the microwave dielectric constant of the material;the effect of the doping of Sn⁴⁺and Ti⁴⁺on the increase of the average lattice energy of YIG is even more obvious,which enhances the bonding force between the ions,and the stacking is more compact,and reduces the chance of the electron jump between the ions,thus reducing the microwave dielectric loss of the material.The Y_3-x-yCa_xBi_yTi_zFe_5-zO₁₂（x=0.09-0.11,y=1.19-1.21,z=0.09-0.11）material obtained by combinatorial ion substitution of YIG with Ca²⁺-Ti⁴⁺and supplemented by Bi³⁺was screened by side-by-side comparisons of the theoretical calculations of the complex bond theory of each combinatorial ion substitution of YIG in the saturation magnetization of 1409 G and a spin-wave linewidth of 3.6 Oe,the performance of the material is effectively enhanced to a microwave dielectric constant of 23.5 and a dielectric loss angle tangent of 4.01×10^-4,but the ferromagnetic resonance linewidth becomes larger at 274 Oe,which limits the practical application of the material.2.Unlike the Ca²⁺-Sn⁴⁺combination substitution in which Ca²⁺enters the dodecahedral crystalline sites to replace Y³⁺and Sn⁴⁺enters the octahedral crystalline sites to replace one Fe³⁺,both ions enter the octahedral crystalline sites to replace two Fe³⁺during the Zn²⁺-Sn⁴⁺combination substitution,which is a more pronounced modulation of the material’s saturation magnetization for a certain range of the same combination substitution amount;the substitution is conducive to promote the material densification and reduce the material porosity,but the enhancement of the chemical bonding ionicity of the material does not play a significant role.Therefore,the combination of Zn²⁺-Sn⁴⁺substitution is conducive to the regulation of the saturation magnetization intensity of the material,reduce the ferromagnetic resonance line width,but the effect on the microwave dielectric properties is not obvious.The ferromagnetic resonance linewidth of the sample at a combined substitution of 0.3 is 37 Oe,the saturation magnetization is 1955 G,its microwave dielectric constant is 16.4,the dielectric loss angle tangent is 4.40×10^-4,and the spin-wave linewidth is 1.5 Oe.3.In order to enhance the high power tolerance of YIG,the mechanism to improve the spin-wave linewidth of the material was investigated based on the fast-relaxation ion substitution,grain size control and other measures.Taking Y_2.5Sr_0.5Fe_4.5Ti_0.5O₁₂ as the basic formula,the spin-wave linewidth of Dy³⁺and Ho³⁺-substituted materials under the same process conditions was comparatively investigated,and it was found that the substitution resulted in lattice distortion due to the larger ionic radius of Dy³⁺and Ho³⁺compared with that of Y³⁺,which improved the magnetocrystalline anisotropy of the material,and the magnetocrystalline anisotropy constant of the material was effectively increased to 7.47×10³ erg/cm³,but there is little difference in the effect on the saturation magnetization under similar substitution;the fast relaxation ions Dy³⁺and Ho³⁺have larger orbital angular quantum numbers,which enhance the spin-orbit coupling,and the coupling between the energy of the spin wave and the lattice energy is faster,which can reduce the relaxation time of the spin wave,and is conducive to increasing the spin-wave linewidth of the material.Dy³⁺has a larger eigenvalue coefficient,so the effect of boosting the spin-orbit coupling within the crystal is more pronounced and exhibits a larger spin-wave linewidth.The average grain size and corresponding spin-wave linewidth of samples with different sintering temperatures,different holding times,and different amounts of fast-changing ion substitution were comparatively analyzed.It shows that the spin wave linewidth of the samples with an average grain size of 6-6.5μm or more is mainly affected by ion substitution,and that of samples with an average grain size of less than 6-6.5μm is mainly affected by grain size.1300°C and a holding time of10 h of the 1300°C and 10 h of heat preservation,the average grain size of the material can be controlled to below 6-6.5μm,which can reduce the average free range of the spin wave propagation and the transition time,and improve the spin wave linewidth of the material.When the substitution amount of Dy³⁺is 0.06,the average grain size of the sample is 4.8μm,and the spin-wave linewidth is increased to 18.7 Oe,and the ferromagnetic resonance linewidth is 71 Oe.Therefore,the fast-relaxation ion substitution and the control of the grain size can effectively improve the spin-wave linewidth of the material,while the improvement of the spin-wave linewidth will lead to the increase of the ferromagnetic resonance linewidth.4.The microwave magnetic and dielectric properties of YIG were investigated in this dissertation through ion substitution and preparation process modulation.The results show that the complex bond theory can be used to analyze and establish the connection between the microwave dielectric properties of YIG and the nature of ionic bonding and the changes in the electronic structure of crystals,and it is found that the ionic and lattice energies of the chemical bonding of the material can be improved significantly by the combined ionic substitution of Ca²⁺-Ti⁴⁺,which is more conducive to the improvement of the microwave permittivity of the material;and the measures such as fast-relaxation ionic substitution and the control of the crystalline grain size can improve the spin-wave linewidth of the material effectively.