Research On Crystal Structure And Physical Properties Of Cation Doped SrTiO₃Magnetooptical Films

The integrated circuit, which is one of the most important scientific andtechnological achievements of the20thcentury, promoted the rapid development ofelectronic technology. However, due to the constraints of the electron mobility in thework rate, power consumption and heat dissipation, etc., integrated circuitsgradually can not meet the requirements for high-speed operation, low powerconsumption, as well as a large amount of information transmission.Compared withelectrons, photons have no mass and the transmission rate is1500times than theelectron, so the development of optical devices will have the revolutionary influenceto solve the present power consumption, heat dissipation and bottleneck ofperformance improvement. Integrated optical device have higher efficiency,operation speed and economy advantage compare with system composed by discretecomponents. Therefore, to integrate the optical device elements such as lasergenerator, modulator, optical waveguide and detector on Si or III-V semiconductorsubstrates has attracted wide attention. However, Nonreciprocal photonic devicesincluding optical isolators and optical circulators are the only absent integratedoptical device due to absence of magneto-optical materials which both have thegood figure of merit and matching ability with semiconductor substrates such as Si.In the present work, the crystal structure, magnetic, optical and magntoopticalproperties of Fe:SrTiO₃perovskite films grown on （LaAlO₃）_0.3（Sr₂AlTaO₆）_0.7--LSATsubstrate with different Fe contents, laser energy density and depositional thicknesswere investigated. The Fe doped SrTiO₃films which B sites substituted by differentFe contents, were perovskite-structureepitaxial films and no second phase orimpurity phase. With increasing Fe concentration, lattice parameters c and c/a ratiowere increased. The films showed in-plane compressive stress. The saturationmagnetization （Ms）, increased with increasing Fe concentration and reachedmaximum when Fe concentration was40%. The coercivity fields and anisortropyincreased with Fe content. The mechanism for room temperature ferromagnetismwas mainly Super-exchange and Double-exchange effects between Fe-O-Fe ionpairs. The saturation Faraday rotation increased with increasing Fe content whichconsistent with magnetization curve. The optical transmittance at both visible andinfrared wavelength increased with increasing Fe content, meanwhile, the band gapincreased. The Sr(Ti_0.6Fe_0.4)O₃--STF40film which40at.%Fe doped into B siteshave good figure of merit,¹.1-1.3deg/dB.With the increasing laser energy density, the lattice parameters c and c/a ratioof STF40film decreased, meanwhile, the saturation magnetization, coercivity fields,anisortropy and saturation Faraday rotation were also decreased. The optical transmittance at both visible and infrared wavelength increased with increasing laserenergy density. The XRD of film was single peak when the depositional thicknesswas thin. When the film thickness exceeded a critical value, the strain was partiallyrelaxed and became double peaks in XRD.The STF40perovskite film grown on Si substrate by CeO2/YSZ buffer layerwhich lattice diagonal atoms of films after rotate45°matched with lattice adjacentedges instead of cubic on cubic method. Both the film and substrate wereperovskite-structure epitaxial films without second phase or impurity phase. Thefilms grown on CeO2/YSZ/Si had similar magnetic properties with that on LSAT.The effect of A site La,Ce and B site Zr, Ga doped Sr(Ti_0.6Fe_0.4)O₃by cationdoping method on crystal structure, physical properties and figure of merit wereinvestigated. The results showed that the A site La, Ce doped Sr(Ti_0.6Fe_0.4)O₃filmswere perovskite epitaxial films. The lattice parameters c and c/a ratio of the filmsincreased with increasing La,Ce concentration.There were no second phase andcluster in the films, the elements distribution of films were homogeneous withoutelements diffusionat the interface of films and substrates. The XPS results show thatCe ions showed a dominant3+valence state, and acted as donors on the Sr2+site （Asite） in the perovskite lattice.Ce Theoptical band gap widened and the Fermi levelmoved toward the vacuum level with increased or La content;meanwhile the Ti andparticularly the Fe ions were driven to a lower valence state. The saturation Faradayrotation increased with increasing La, Ce concentration which consistent withmagnetization curve. The optical transmittance at both visible and infraredwavelength decreased with increasing La, Ce content. The low temperaturemagnetic properties of the films showed spin-glass behavior. The peak position ofzero-field-cooling curves of films shifted with strain state. The figure of merit of Asite La, Ce doped Sr(Ti_0.6Fe_0.4)O₃were not improved due to rapid decreasing ofoptical transmittance.The lattice parameters c, the saturation magnetization,coercivity fields,anisortropy and saturation Faraday rotationof Ga Substituted Sr(Ti_0.6Fe_0.4)O₃in Bsite which acted as acceptors decreased with increasing Ga concentration. The Tiand the Fe ions were driven to a higher valence state, and the optical transmittanceincreased with increasing Ga contents. The Zr Substituted Sr(Ti_0.6Fe_0.4)O₃in Bsiteacted as donors due to the average valence state of Zr was higher than that of Ti.The films were perovskite films, and the lattice parameters c and c/a ratioincreased with increasing Zr contents. The Ti and the Fe ions were driven to a highervalence state. The saturation magnetization increased at first and then decreasedwhich reach the maximum at20at.%Zr content. The optical transmittance decreased with increasing Zr contents.In conclusion, the Fe and Ti valence state played a important role in figure ofmerit of the Fe doped SrTiO₃perovskite films. The figure of merit and opticaltransmittance of donor doped Fe:SrTiO₃decreased due to the Ti andFe ions weredriven to a lower valence state. The figure of merit a of acceptor doped Fe:SrTiO₃increased due to the improvement of optical transmittance. The figure of merit ofSr(Ti_0.2Ga_0.4Fe_0.4)O₃could reach4⁶.7deg/dB which could be important candidatefor integrated optical isolators.