Preparation And Design Of Single Crystal Garnet Thin Film And Its Application In Magneto Optical Switch

Liquid phase epitaxy（LPE）has so far been one of the best techniques for the preparation of single crystal garnet films.A lot of research shows that Bi³⁺can replace Y³⁺ions in yttrium iron garnet（YIG）to grow Bi-substituted garnet（Bi:YIG）films.Bi:YIG film has larger specific Faraday rotation angle than that of pure YIG,and its easy magnetization axis can easily tuned to out of plane orientation,which allows to operate under small external magnetic field.Thus Bi:YIG film meet the demand of miniaturization and energy saving of magneto-optical devices.Because the ionic radius of Bi³⁺（108（?））is larger than that of Y³⁺（90（?））,the doping of Bi³⁺will lead to lattice expansion of the garnet film,resulting in lattice misfit with the gadolinium gallium garnet（GGG）substrate.In order to neutralize the lattice expansion caused by Bi³⁺,Tm³⁺（86.9（?））with smaller ionic radius than Y³⁺（90（?））is selected to co-doping.Meanwhile,Ga³⁺is doped to replace Fe³⁺at 24d site of tetrahedron in YIG to reduce the saturation magnetization intensity of the garnet film and thus the saturation field of the film can be reduced to a certain extent.In this paper,the single crystal（TmBi）₃（FeGa）₅O₁₂ films with different growth temperatures and thicknesses are designed and prepared by LPE method.Based on the analysis of the magnetoanisotropy theory of garnet films,the effects of lattice misfit,growth temperature and stress on the magnetoanisotropy of（TmBi）₃（FeGa）₅O₁₂ films are investigated.Firstly,the hysteresis loop,lattice mismatch and Bi³⁺content of（TmBi）₃（FeGa）₅O₁₂garnet films are measured and characterized.The results show that the garnet films always exhibited out-of-plane anisotropy;when the thickness of the epitaxial film is more than 1μm,the influence of shape anisotropy on the magnetoanisotropy can be ignored.Stress-induced anisotropy dominated the variation of magnetic anisotropy compared to growth-induced anisotropy.Secondly,Faraday test is carried out on（TmBi）₃（FeGa）₅O₁₂ film and the Verdet constant of the garnet film is calculated as 11.8×10⁴rad/Tm@1064nm.It is 3000 times higher than that of TGG,which shows that（TmBi）₃（FeGa）₅O₁₂ single crystal films have great potential for development in magneto-optical devices.Based on the analysis of magneto-optical properties and film quality,it is concluded that a growth temperature of 893℃ is the optimum growth temperature,and a Faraday rotor in a magneto-optical switch was fabricated.When the test wavelength is 1310 nm,the specific Faraday rotation angle is 0.068°/μm,and the external saturation magnetic field is 70 G_S.The（TmBi）₃（FeGa）₅O₁₂ single crystal film has a larger than specific Faraday rotation angle and a smaller external magnetic field,which can meet the design requirements.Finally,the magneto-optical switch working at 1310nm is designed,simulated and processed.