Investigation On Magnetic, Electrical And Magnetoelectric Coupling Properties Of Doped M-type Hexaferrite

M-type hexaferrite has a wide range of applications in THz band microwave devices,high-density memory and so on.Results show that the substitution of Fe³⁺in M-type hexagonal ferrite can change the magnetic structure of the material,which makes the material exhibit soft magnetic properties.For example,Sc³⁺substituted M-type barium ferrite has a widely multiferroic application prospect at room temperature.But its magnetoelectric coupling and magnetodielectric properties near room temperature have not been well discussed.As the electronic materials and devices tending to be miniaturized and high-frequency,the demand for magnetic material is also gradually expanding from the bulk to the film.Therefore,the preparation of high-quality M-type hexaferrite thin film material and a comprehensive investigation on magnetic,magnetodielectric and magnetoelectric coupling properties of the thin film become very important.In view of the above problems,this paper focuses on the study of magnetic,magnetoelectric coupling,and magnetodielectric properties of Sc³⁺substituted M-type barium ferrite around the room temperature.The results are as follows:Firstly,Sc³⁺substituted M-type hexaferrite BaFe_10.2Sc_1.8O₁₉ was prepared by the solid-state reaction method.The phase formation and magnetic property evolution processes of this ferrite have been investigated during the sintering progress.It has been found that the magnetic property evolution processes agree well with the phase formation.The sintered product contains not only the single phase BaFe_10.2Sc_1.8O₁₉ until the sintering temperature ups to 1200?.With the increasing sintering temperature,the substitution of Sc³⁺for Fe³⁺will affect the exchange interaction of iron atoms in M-type ferrite,which can change the magnetic structure of the material and realizing the change of magnetic properties macroscopically.Secondly,the magnetic properties of BaFe_10.2Sc_1.8O₁₉ polycrystalline bulk were investigated.The results show that the coercive field and the remanence ratio decrease with the increasing temperature,the saturation magnetization increases firstly and then decreases.In addition,an increase in the applied magnetic field will lead to a decrease in the conical magnetic structure transition temperature T_cone.At room temperature,the magnetic moment of BaFe_10.2Sc_1.8O₁₉ can be obviously manipulated by a small electric field,which indicates a strong magnetoelectric coupling effect in this material.Besides,large magnetocapacitance effects are also observed around the room temperature.At low frequencies,the Maxwell-Wagner type magnetoresistance effect dominates the magnetocapacitance.At high frequencies,the inverse Dzyaloshinskii-Moriya interaction induced magnetoelectric type spin-phonon coupling is the dominant factor for the magnetocapacitance.Thirdly,we have prepared a series of epitaxial Sc³⁺substituted BaFe_12-xSc_xO₁₉ thin films,and studied the substitution influences on its crystal structure and magnetic properties.The results show that the lattice constant c of the thin film increases with the increasing substitution amount of the larger radius Sc,but the saturation magnetization and the coercive field decrease,which is similar with the polycrystalline bulk BaFe_12-xSc_xO₁₉.At last,the magnetodielectric effects of BaFe_10.2Sc_1.8O₁₉ thin film have been investigated around the room temperature.The results show that the magnetodielectric effect in the film is highly frequency and temperature dependent at room temperature.Frequency dependent magnetodielectric analysis shows that the magnetoresistive type magnetodielectric effect exists only in the low frequency region?f<100Hz?and is very small.When the frequency is higher than 1 kHz,two magnetodielectric peaks are observed which are contributed by the interfacial polarization effect?1 kHz<f<100 kHz?and electric dipole rotation effect?f>100 kHz?,respectively.Further temperature dependent analysis shows that the Dzyaloshinskii-Moriya dipoles dominate the magnetodielectric effect in the temperature region below T_cone?306K?,while the lattice dipoles dominate the magnetodielectric effect above T_cone.At the temperature near T_cone,both the Dzyaloshinskii-Moriya and lattice dipoles contribute to the magnetodielectric effect.