Research On Regulatory Mechanism Of Dynamic Magnetic Property In The Multiferroic Materials

As a new multifunctional material,the multiferroic materials have two or more ferroics.The coupling between ferroelectric?FE?and ferromagnetic?FM?produces a new magnetoelectric effect?ME?.The magnetoelectric effect make it as the hotspot in multiferroic materials research in recent years.This new magnetoelectric effect materials provide a new method for miniaturization design of microwave device and intelligent absorption design of electromagnetic wave.It has wide applications in adjustable microwave device and electromagnetic absorption.In this dissertation,we studied on composite multiferroic material 2-2 multi-iron heterostructure.In order to overcome the limitation of the single control of ferroresonance frequency at the electric field in the 2-2 multiferroic heterostructures,a series of studies have been carried out on ferromagnetic resonance bandwidth and ferromagnetic resonant frequency amplitude in the 2-2 multiferroic heterostructures.FeGaB monolayer,FeCoB/SiO₂/FeGaB sandwich structure and FeCo B-SiO₂ nano granular films were prepared on the piezoelectric substrate by magnetron sputtering.We have proposed the regulatory mechanism based on the converse piezoelectric effect.The stress magnetic anisotropy at different electric field could influence on the magnetism of magnetic materials.On the basis of the above,the transfer mode of stress in the sandwich structure and the nanoparticle membrane have been studied.Meanwhile,the crystal structure and macromagnetism of BiFeO₃ are discussed.The mechanism of macroscopic magnetic enhancement bases on the inhibition of helical spin magnetic structure.The main content and innovation are as follows:1.We have proposed the composite structure about the monolayer FeGaB films and single-crystal piezoelectric materials.Based on the nonvolatile and reversible lattice distortion caused by 71° and 109° ferroelectric domain switching in the piezoelectric substrate,the magnetic properties of FeGaB films under different electric fields were studied systematically.The composite structure can retain a part of the regulation performance and return to the initial state under the reverse electric field.It is important to further reduce the energy consumption.2.We have proposed the composite structure about FeCoB/SiO₂/FeGaB sandwich structure and the single crystal piezoelectric material.Based on the analysis of Young 's modulus of different films in Fe Co B/SiO₂/FeGaB sandwich structure,the stress transfer mode of multilayer structure was proposed.This research was of great significance to the intelligent regulation of the electromagnetic wave absorption bandwidth.3.We have proposed the composite structure about FeCoB-SiO₂ nano granular films and the single-crystal piezoelectric materials.In order to overcome the mismatching of the dielectric constant and the magnetic permeability in the electromagnetic wave absorbing material,the stress transfer mode of FeCo B-SiO₂ nano granular films was proposed by the strain response of piezoelectric strain under the electric field.This framework realizes the tuning of amplitude value of the imaginary part ??by E-fields in a certain frequency range and provided a new effective method for balancing the dielectric constant and the magnetic permeability of the electromagnetic wave absorbing material.4.We have proposed the preparation method of Y doping BiFeO₃ and the regulatory mechanism of macroscopic magnetism enhancement.Based on the change of the lattice parameters of Bi_1-xY_xFeO₃,the relationship between the crystal structure of BiFeO₃ and the amount of Y dopant was established.Combined with the M?ssbauer spectroscopy,we have proposed the regulatory mechanism of inhibition of helical spin magnetic structure.It has provided an effective method to enhance the magnetoelectric effect of BiFeO₃.In this dissertation,the regulation of nonvolatile and reversible,ferromagnetic resonance bandwidth and ferromagnetic resonance frequency amplitude of the magnetic materials were discussed.Meanwhile,the changes of mechanism of microwave dielectric and magnetism in BiFeO₃ is discussed in detail.These studies lay a new foundation for the application of multiferroic materials in microwave devices and electromagnetic wave absorption and had an inportant theoretical significance.