Design,synthesis And Magnetoelectric Control Of Transition Metal Oxides (Mn_1-xZn_x)₃Ta₂O₈ And SrCo₂M（PO₄）₃(M=Fe³⁺,Cr³⁺)

The magnetoelectric（ME）materials can realize the mutual control of electricity and magnetism,which is important in physics and applications such as information storage,communication technology,medicine,and military fields.In the past two decades,ME materials have been the focus of condensed matter physics,and fruitful results have been achieved in this field.Nevertheless,the performance of present multiferroic materials is still poor and far from applications.The exploration and research of new materials are still major tasks.In this thesis,we focus on Mn₃Ta₂O₈,SrCo₂Fe（PO₄）₃,and SrCo₂Cr（PO₄）₃ to explore the manipulation of ME effect and novel ME materials.The specific arrangement of the thesis is as follows:In the first chapter,the history of magnetic materials and the categorization of magnetism are outlined,followed by a brief description of ferroelectric materials.Next,the classification of multiferroic materials and their characteristics are described in detail.Finally,we discuss linear magnetoelectric materials and their disadvantages.The second chapter mainly described the experimental method,including synthesis method and equipments involved in this thesis.The main contents are as follows:the processes of the traditional high-temperature solid-state reaction method,the structural characterization of the samples utilizing X-ray powder diffraction（XRD）,and the characterization of the magnetism,specific heat,and electrical properties of samples using a completely liquid helium-free integrated physical property system（PPMS）.The third chapter is the systematical research of the impact of Zn doping on the crystal structure,magnetic properties,and ME coupling of the linear ME material Mn₃Ta₂O₈.According to the experimental results,the magnetic phase transition temperature of(Mn_1-xZn_x)₃Ta₂O₈ gradually decreases with the increase of the Zn content x.Meanwhile,the ME effect of(Mn_1-xZn_x)₃Ta₂O₈ changes significantly,indicating that the material transforms from linear ME material to multiferroic material.This work is benifial to the exploration of linear ME materials and multiferroic materials.The fourth chapter focuses on the crystal structure,magnetic properties,specific heat,and ferroelectric polarization of SrCo₂Fe（PO₄）₃.According to the experimental results,the space group of SrCo₂Fe（PO₄）₃ is Imma.And SrCo₂Fe（PO₄）₃ undergoes an antiferromagnetic phase transition at T_N～50.5 K.The specific heat and magnetic entropy of SrCo₂Fe（PO₄）₃ suggests that the Co²⁺is in high spin state（S=3/2）.This work will help the exploration of new magnetic materials.In the fifth chapter,SrCo₂Cr（PO₄）₃ compounds were successfully synthesized using Cr instead of Fe element,and their structural,magnetic,and specific heat properties were systematically researched.The space group of SrCo₂Cr（PO₄）₃ is Imma.And SrCo₂Cr（PO₄）₃ undergoes a ferrimagnetic phase transition at T_N～55 K.According to the analysis of specific heat and magnetic entropy,the Co²⁺in SrCo₂Cr（PO₄）₃ is in high spin state（S=3/2）.Here we realize the transformation of antiferromagnetic materials into ferrimagnetic materials by replacing Fe with Cr,which will contribute to the search of new magnetic materials.The sixth chapter is a summary and outlook of this thesis.