Magnetic Properties Of Double Perovskite Ba₂MnTeO₆

As we known,there are many degrees of freedom in the transition metal oxides,including electron,orbital,spin,and crystal lattice,that compete and couple with each other,which can lead to plenty of fascinating physical properties,such as rich magnetic properties,metal insulator transition,and ferroelectricity,superconductivity,magnetic multiferroics,giant magnetoresistance effect et al.Among so many research fields about the transition metal oxides,the one about Triangular Lattice Antiferromagnets（TLAFs）attracts much attention of us.Due to the peculiar triangular structures of transition metal ions,spin frustration could be found in TLAFs.Furthermore,since the space symmetry can be broken by this kind of magnetism,ferroelectricity appears as well,which gives the possibility for us to search for magnetic multiferroic materials.Although much progresses have been made in the past years in the triangular lattice antiferromagnets,considering the attraction of searching the strong coupling material of magnetism and ferroelectricity,it is still worth us keeping researching it in some new materials.The study of thesis will carry out in Ba₂MnTeO₆ which is a double perovskite oxide material with the triangular lattice.Firstly,the double perovskite oxide Ba₂MnTeO₆ and its doped samples are prepared with high temperature solid state method.Then using both the experimental and computational methods,its morphology and magnetic are studied.The whole thesis is organized as follow:In the first chapter,the research background,crystal structure and doping effect of double perovskite oxides are introduced.Above all,the frustrated magnetic phenomenon in the triangular antiferromagnets is illustrated in detail.In the second chapter,the preparation and characterization methods used in our research are briefly introduced,including instruments and principles of material structure characterization,morphology characterization,magnetic characterization,optical performance characterization.Besides,the density functional theory calculation and Monte Carlo methods are introduced as well.In the third chapter,the preparation method of Ba₂MnTeO₆ sample is introduced.After prepared the sample,the structure and morphology are characterized and analyzed by a series of experimental methods.And then the magnetic properties in Ba₂MnTeO₆ is studied by a series of characterizations.In addition,first-principles calculation and Monte Carlo simulation are applied to study of the ground magnetic state at low temperatures.Combined both of these methods,our results prove that Ba₂MnTeO₆ has a spin-like glass behavior at temperatures below 110 K and an antiferromagnetic phase at 23 K.In the fourth chapter,the structural characteristics and magnetic properties of doped double perovskite Ba_2-xA_xMnTeO₆（A=K,La）are studied.The effects of electron and hole doping on the magnetic properties of Ba₂MnTeO₆ samples was analyzed through doping different ions in the A site.Our studies show that the magnetic transition occurs from antiferromagnetic state to ferrimagnetic state no matter what kind of doping is introduced.The fifth chapter is devoted to the conclusion and perspectives to the future work.