Study On Magnetic And Magneto-optical Properties Of Doped Yttrium Iron Garnet Thin Films

Yttrium iron garnet?YIG?thin film?s unique magnetic and magneto-optical properties offer great opptunities for future magnonic devices and optical isolators.In the field of current research on nanoscale YIG thin films,perpendicular anisotropy thin films and thin films with high figure of merit are the material basis of miniaturizing the scale of magnonic devices and integrating magneto-optical devices.YIG has in-plane easy anisotropy and low magneto-optical effect,in this thesis,we modified the mangetic and magneto-optical properties by ions doping to deal with those issues.We present three studies on doped yttrium iron garnet thin films growth using pulse laser deposition?PLD?and their strucuture,magnetic and magneto-optical characterization.We first epitaxially grown manganese doped YIG films?Mn:YIG?on Gd₃Ga₅O₁₂?GGG,111?substrates.Lattice-induced strain and enhanced magentostriction dueto Mn doping lead to stronger magnetoelastic anisotropy and tune the magnetic anisotropy of YIG thin films.In particularly,we realized perpendicular anisotropy in high concentration Mn:YIG films,with narrow ferromagnetic resonace?FMR?lindwidth of only 65 Oe.Using FMR techniquies,we were able to quantitatively characterize the mangetic anisotropy terms of Mn:YIG thin films and a continuous increase of out-of-plane magnetic anisotropy from 644.4 Oe of YIG films to 1337.5 Oe of Y₃(Fe_3.88Mn_1.12)O₁₂2 films is observed.We also managed to control the magnetic anisotropy of polycrystalline Ce doped YIG?Ce:YIG?films using thermal-induced strain and Dy doping.We fabricated Dy doped Ce:YIG?DyCe:YIG?thin films with single-step deposition method,and X-ray diffraction?XRD?suggests that all DyCe:YIG thin films crystalline to garnet phase.Dy doing effectively tunes the anisotropy of Ce:YIG with the out-of-plane saturation field decreases from 2820 Oe to 540 Oe,and in the mean time,the DyCe:IYIG films have high Faraday rotation,which can serve as popential material for TE mode integrated magneto-optical devices.On the other hand,by incorporating Ce³⁺into dodecahedral sites and contolling the concentration of Fe²⁺ions,we succeed in integrating polycrystalline Ce:YIG films with high Faraday rotation and low optical loss.We used strip-loaded waveguide to characterize the optical loss of YIG thin films and optimized the figure of merit?FoM?of Ce:YIG thin films.We reported that the crystalline state of YIG thin films effects the scattering loss of films and the existence of Fe²⁺in Ce:YIG films could significantly increases the optical loss of films.And We optimized the FoM of Ce:YIG films,FoM=39.8 deg/dB,with 50 nm YIG seed layer and 10 mTorr O₂depostion pressure of Ce:YIG thin films.Finally,We designed an integrated Mach-Zehnder type optical isolator with uniaxial magnetic field.The isolator works in TM modes at 1548 nm wavelength,with maximal isolation ratio of 22.5 dB.The device?s 20 dB isolation bandwidth is about 1nm,and its insertion loss is about 8 dB,which may be used in a range of monolithically integrated photonics devices on silicon,enabling wafer-sacle integration of non-reciprocal devices for future silicon photonic systems.