Study On The Powder Preparation And Crystallization Behavior Of Rare-earth Iron Garnet

The garnet-structured R₃Fe₅O₁₂(RIG)is a kind of magnetic functional material and has a wide range of applications in many fields.The RIG crystal represented by YIG shows excellent magneto-optical characteristics in the near-infrared band,and has also been used in the fields like high-performance magneto-optical devices(optical isolators and magneto-optical switches,etc.),optical communications,and optical information processing.It also shows characteristics with narrow line width of ferromagnetic resonance,extremely low magnetic damping,with potential applications such as microwave oscillators and microwave filters.However,the growth of high-quality YIG crystals is very difficult due to the inconsistent melting characteristics and complex phase relationship.Based on these issues,this paper is mainly conducted with the following results.1.A series of Tb₃Fe₅O₁₂(Tb IG)and Tb_3-xBi_xFe₅O₁₂(Bi:Tb IG)powders were prepared by solid-phase method and sol-gel method,and their crystal structure and room temperature magnetic properties were systematically analyzed and discussed.For solid-phase synthesis,using Fe₂O₃,Tb₄O₇,Bi₂O₃ as raw materials,it is necessary to sinter at 1320?to obtain pure phase powder.In the sol-gel method,citric acid is used as the complexing agent,and the ratio of metal ions is 1.2:1.When the heat treatment temperature reaches 800?,Tb_3-xBi_xFe₅O₁₂powder with pure phase garnet structure(x=0,0.1,0.2,0.3,0.6,0.9).The TIG powder is ferromagnetic at room temperature.After the substitution of bismuth ions,the saturation magnetization Ms and the residual magnetization Mr of Tb_3-xBi_xFe₅O₁₂ increase with the increase of Bi³⁺content,which is mainly caused by bismuth ions Caused by structural distortion and Fe³⁺—O^2-—Fe³⁺superexchange interaction.2.YIG crystal was grown by the flux method with the lead-free based Bi₂O₃ as the flux.The crystallization behavior of YIG has been systematically studied by adjusting the solution composition and and the growth paramters.Bi₂O₃ is the main component of flux,and it is about 45-60 wt%of the whole solution.It melts at about 1200-1330?,and slowly crystalizes with the decreasing temperature of 1-3?/h.A series of YIG crystalline particles have been obtained under these growth conditions.YIG crystals usually show hexagonal growth hillock.In the cubic system,[111]is the close packing direction of atomic arrangement.Both the atomic arrangement and corresponding diffraction image in the(111)face take the shape of hexagon.Meanwhile,[111]is also the most possible magnetization direction for cubic YIG crystal.Moreover,step growth was also usually observed during the growth,which is possibly resulted from the screw dislocation.