Preparation And Characterization Of Yttrium Iron Garnet Magneto-optical Ceramics

The magneto-optical modulator is an indispensable strategic device for modern optical fiber communication and laser systems.The typical magneto-optical material YIG(Y₃Fe₅O₁₂)will be applied extensively in the 5G optical communication system and mid-infrared laser technology in the future for their excellent Faraday effect and optical properties in the infrared band.However,till now,only the YIG single crystals can be used in the magneto-optical modulation and magneto-optical isolation in the mid-infrared laser technology for their outstanding infrared transparency,and the needed YIG magneto-optical crystals in our country are dependent on imports.At the same time,due to the difficulty and the long growth cycle in the YIG crystal’s preparation,the size of the YIG single crystal is always small,which is difficult to satisfy the requirements of the large-diameter and high-throughput mid-infrared laser system.Therefore,the infrared transparent YIG magneto-optical ceramics with high-quality and large-scale has been proposed to study,which would replace the YIG single crystals applied in the magneto-optical modulator and promote the development of mid-infrared laser technology.In this work,YIG(Y₃Fe₅O₁₂)was selected as the principal material system,and the transparent YIG magneto-optical ceramics were synthesized by a solid-state reaction process.To eliminate the micro-defects（porosity,impurity phase）in the material,restraint the valence change of Iron,and increase the solid solubility of the functional doping ion,the series YIG ceramics were sintered by the conventional sintering method,the hot pressing sintering method,and the hot isostatic pressing sintering method respectively.The YIG magneto-optical ceramics with good infrared transparency were obtained,and the phase structure,microstructure,magnetic properties,magneto-optical properties,and optical transparency of the YIG ceramics were investigated and discussed systematically.The main results are as follows:1.The YIG magneto-optical ceramics were prepared by the conventional sintering method.The effects of the raw material powder morphology and the sintering temperature on the material density,phase structure,grain size,and magnetic properties of YIG ceramics were investigated systematically.The optimized sintering temperature range was determined.2.A combination of atmospheric hot pressing sintering process and hot isostatic pressing sintering process is utilized to obtain the high-transparency YIG magneto-optical ceramics.The density of the ceramic samples measured by the Archimedes method is almost the same as the theoretical density（5.17g/cm³）;the YIG ceramic samples show the pure garnet phase structure and dense microstructure,which ensure the material an exceptional optical performance in the mid-infrared band（transmittance is≥75.0%（λ:2500nm;sample thickness:1.0mm））;the Faraday rotation angle of the YIG magneto-optical ceramic sample was measured to be173.5deg/cm,which is almost consistent with that of the reported YIG single crystal（174.0deg/cm）.3.A series Bi³⁺modified YIG ceramics(Bi_xY_1-xFe₅O₁₂,x=0,0.3,0.6,0.9)have been prepared to optimized the material magneto-optical property.The effects of the Bi³⁺content on the optical quality,magnetic properties,and magneto-optical properties of the samples were investigated and discussed.With the Bi³⁺content increasing,although a small amount of Bi³⁺began to stay at the grain boundary to form the impure phase and further decrease the material infrared transmittance,the most of the doping Bi³⁺ions entered the garnet crystal lattice.This makes the magneto-optical property of the YIG ceramics enhanced obviously.It has been found that when the Bi³⁺doping content increases per 1 mol%,the Faraday rotation angle of the Bi³⁺modified YIG ceramic sample changes-49.0 deg/cm and-30.2 deg/cm at the wavelengths of 1064nm and 1550nm respectively.