Ce-substituted Yttrium Iron Garnet Research Articles

Polycrystalline to preferred-(100) single crystal texture phase transformation of yttrium iron garnet nanoparticles.

Nanocrystalline Ce-substituted yttrium iron garnet (YIG) powders of different compositions, Y3−xCexFe5O12 (0 ≤ x ≤ 2.0), were synthesized by a combination of sol–gel auto-combustion and solid-state synthesis techniques. The as-obtained powder samples were sintered at 1150 °C for 10 h. The garnet structure formation is confirmed by the X-ray diffraction pattern, which shows that the calculated lattice parameter increased for x = 1.0 and shows a decreasing trend for x ≥ 1.0 with the addition of cerium ions. The lattice parameter increased from 12.38 Å to 12.41 Å for x ≤ 1.0 whereas it decreased from 12.412 Å to 12.405 Å with the cerium composition for x > 1.0. The average particle size determined by high resolution transmission electron microscopy is in the range of 50 to 90 nm and found to increase with the substitution of cerium ions in YIG. The room temperature magnetic parameters such as saturation magnetization, coercivity and remanence magnetization are greatly affected by the substitution of cerium ions. The values of saturation magnetization decrease from 25.5 to 15 emu g−1 whereas coercivity increases from 1 to 28 Oe with the substitution of cerium ions. The pure YIG sample shows polycrystalline nature that changed towards a single-crystal structure leading to a preferred-(100) orientation with the Ce substitution. The change from a ring to a spotty pattern observed in SAED confirmed the crystalline phase transformation and is well supported by HRTEM and magnetic measurements. The behavior of magnetic and electrical properties is well supported by the poly- and single-crystalline nature of YIG and Ce-YIG, respectively. The crystal structure transformation in YIG brought about by Ce substitution could unveil enormous opportunities in the preparation of single-crystal materials from their polycrystalline counterparts.

Influence of erbium on the structural, optical and magnetic properties of sol–gel Ce: YIG films

Sol–gel Y2.8-xCe0.2Er x Fe5O12 (x = 0.0, 0.2, 0. 4, 0.6, 0.8 and 1.0) nanofilms were successfully prepared for their potential use in nonreciprocal magneto-optical devices, such as isolators and circulators. The effect of Er-doped Ce-substituted yttrium iron garnet (Ce:YIG) was investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), UV–vis spectrophotometry and vibrating sample magnetometry (VSM). Analysis of the diffractograms indicated a cubic garnet structure and the incorporation of the Er3+ ions into the Ce: YIG. The absorption bands in IR spectra revealed the fingerprint of the YIG structure in the obtained films. The optical transparency of the Er-doped Ce:YIG samples was above 98% in the visible and near infrared region wavelengths. All samples were soft ferrimagnetic films, as indicated by their hysteresis loops and low magnetic coercivity fields (~50 Oe). As more erbium ions were introduced, the saturation magnetisation decreased and the magnetic coercivity increased. These findings suggest that Er-doped Ce:YIG films may have a promising role in magneto-optical applications.

Magnetic and Magneto-optical Properties of CeYIG Thin Films Grown by Pulsed Laser Deposition on Quartz Substrates

We report the growth of Ce-substituted yttrium iron garnet (CeYIG) thin films deposited by pulsed laser deposition on quartz substrates. CeYIG exhibits a large Faraday rotation in the near-IR region. Upon investigating the phase composition and the magnetic and magneto-optical properties of the films, we present optimal process conditions for growing CeYIG thin films on quartz substrates. A saturation magnetization (Ms) as high as 159 emu/cm3 was achieved by depositing a Ce0.25Y1.75Fe5O12 thin film at a substrate temperature of 650∘C and a 2-Hz laser pulse rate. Under the same depositing conditions, CeYIG thin films annealed at 800∘C for 40 min provided the largest Faraday rotation (FR) angle of −6000∘/cm by applying an out-of-plane magnetic field. Hence, CeYIG thin film materials show promise for magneto-optical and microwave communication applications.

Structure and Magnetic Properties of Ce-Substituted Yttrium Iron Garnet Prepared by Conventional Sintering Techniques

Y3−xCexFe5O12 (CeYIG) ceramics, with x = 0, 0.15, 0.25, 0.35, 0.45, and 0.5, were fabricated by a conventional ceramic sintering technique. We studied the structures and magnetic fields of a series of CeYIG ceramics using X-ray powder diffraction, a scanning electron microscope, and a superconducting quantum interference device magnetometer. Findings showed that the substitution limit of the concentration of Ce3+ ions in the yttrium iron garnet structure was approximately x = 0.25. An extra CeO2 phase was detected in the ceramic when the addition of CeO2 content overtook the limit. The lattice constants and relative densities increased by increasing the Ce3+ contents in the ceramics. First, the saturation magnetization increased gradually with increases in the substitute concentration of Ce3+ ions and then decreased gradually when x = 0.35, 0.45, and 0.5. Overall, this study showed that the Y3−xCexFe5O12 material with x ≤ 0.15 exhibited excellent magnetic properties. Hence, the material show promise for magneto-optical and microwave communication applications.

First principles calculation on the magnetic, optical properties and oxygen vacancy effect of CexY3−xFe5O12

We report a first principles study on the magnetic and optical properties of Ce substituted yttrium iron garnet (CexY3−xFe5O12) (Ce:YIG) (x = 0.125, 0.25, 0.5, and 1.0). Using density functional theory with Hubbard-U corrections, we demonstrate that Ce3+-Fe3+(tetrahedral) charge transfer is the dominating mechanism of enhanced near infrared absorption in Ce:YIG. In particular, oxygen vacancies are found to be able to stabilize Ce3+ from converting to Ce4+, at the same time reduce two neighboring Fe3+ to Fe2+ which occupy both the octahedral and tetrahedral sites. The formation enthalpy of Ce4+-Fe2+ state is strongly dependent on the distance from the Ce ion to the oxygen vacancy, which is closely related to the local lattice distortion around the Ce ion. This result provides theoretical insight for developing high figure of merit magneto-optical materials for nonreciprocal photonic applications.

Magneto-Optical Faraday Rotation in Ce:YIG Thin Films Incorporating Gold Nanoparticles

We report an experimental study on optical and magneto-optical properties of Ce-substituted yttrium iron garnet thin films incorporating gold nanoparticles. Au nanoparticles were formed by heating Au thin film on cubic quartz and garnet substrates in a vacuum chamber and a Ce:YIG layer was deposited on them by the aid of the pulsed laser deposition method. A large enhancement of the Faraday rotation was obtained in the sample with Au nanoparticles on a quartz substrate and the effect of the substrate material on improving the optical and magneto-optical response of samples were investigated.

Effect of magnetic annealing on magneto-optical properties of Ce : YIG thin films incorporating gold nanoparticles

We report an experimental study on the effect of magnetic annealing process on the optical and magneto-optical properties of Ce-substituted yttrium iron garnet thin films incorporating gold nanoparticles. Au nanoparticles were formed by heating an Au thin film on a cubic quartz substrate in a vacuum chamber and a Ce : YIG layer was deposited on them by the aid of the pulsed laser deposition method. Our results show that magnetic annealing leads to an increase in nanoparticle sizes and directs the magnetization to lie on the sample's surface. Hence, Faraday rotation signal decreases and a sufficient increase in the longitudinal magneto-optical Kerr effect occurs at different oblique incidence angles. Tuning the surface plasmon resonance band by changing the angle of incidence of the excitation light would add an additional degree of freedom and flexibility to the development of magneto-optical sensors.

Effects of Wafer Precleaning and Plasma Irradiation to Wafer Surfaces on Plasma-Assisted Surface-Activated Direct Bonding

The plasma-assisted surface-activated bonding technique enables one to directly bond heterogeneous materials. The surface roughness of wafers is an important factor for achieving bonding. The effects of precleaning and plasma surface activation processes on the surface roughness are investigated for silicon-on-insulator (SOI), Ce-substituted yttrium iron garnet (Ce:YIG), InP and LiNbO3. We found that an appropriate precleaning process reduces the surface roughness. Also, the oxygen plasma irradiation to the wafer surface for 10 or 30 s smoothens the surfaces. We achieved the bonding of SOI–Ce:YIG with a strength greater than 1.8 MPa, which is sufficient for application to silicon waveguide optical isolators and circulators.

Effect of oxidation dynamics on the film characteristics of Ce:YIG thin films deposited by pulsed-laser deposition

Thin films with different compositions of Ce-substituted yttrium iron garnet (Ce:YIG (Y 2CeFe 5O 12)), Ga-doped Ce:YIG (Ce:Ga:YIG (Y 2CeFe 4.25Ga 0.75O 12)), and Gd-doped Ce:YIG (Ce:Gd:YIG (Y 1.6CeGd 0.4Fe 5O 12)) were deposited on gadolinium gallium garnet (GGG (Gd 3Ga 5O 12)) substrates in O 2 or Ar background gas by pulsed-laser deposition (PLD) technique. Crystalline films were obtained at a lower O 2 gas pressure of 20 mTorr or at higher Ar gas pressures of more than 100 mTorr. In addition, the behavior of YO molecules was visualized by two-dimensional laser-induced fluorescence (2D-LIF), in order to investigate the oxidation dynamics in the ablation plume. The oxidation dynamics and the crystallinity had close correlation.

Giant Faraday rotation of blue light in epitaxial CexY3−xFe5O12 films grown by pulsed laser deposition

We report crystalline, magnetic, and magneto-optic (MO) properties of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films epitaxially grown onto single crystal Gd3Ga5O12 (111) substrates using Nd:YAG pulsed laser deposition technique. Oxygen ambient pressure used for the growth is found to be the critical parameter to prepare CexY3−xFe5O12 films with good crystalline and magnetic properties as well as large MO effect. The film fabricated at 50 m Torr oxygen pressure exhibits a maximum Faraday rotation (FR) θF=1.78 and 4°/μm at λ=633 and 430 nm, respectively, a minimum in-plane coercivity Hc=35 Oe, and the narrowest full width at half maximum = 0.06° for the (444) x-ray Bragg reflection rocking curve. The analog of the Verdet constant V=θF/4πMs also found to be dependent on the oxygen ambient pressure reaches a value as high as 1.41°/μm kG at 633 nm, suggesting that this material is useful for MO applications. The energy dispersion FR spectra, measured over visible region 400 to 840 nm, clearly demonstrate that Ce substitution prominently enhances Faraday effect at 690 and at 430 nm blue-wavelength region.

Magnetic and Magneto-Optic Properties of Pulsed Laser Deposited CexY3−xFe5O12 Films

AbstractWe present experimental studies of crystalline, magnetic, and magneto-optic (MO) properties and their correlation with the processing parameters of Ce-substituted yttrium iron garnet (CexY3−xFe5O12) thin films grown epitaxially onto single crystal Gd3Ga5O12 (111) substrates by Nd:YAG pulsed laser deposition technique. Rutherford backscattering (RBS) analysis and microprobe energy dispersive spectrometry (EDS) prove the background oxygen pressure, used for films growth, control films stoichiometry. Oxygen ambient pressure appears to be an important parameter to grow CexY3−x, Fe5O12 films with good crystallinity, magnetic properties, as well as enhanced MO effect. It is found that the film fabricated at 50 mTorr oxygen pressure exhibits a maximum Faraday rotation (FR) øF = 1.78 deg/νtm at λ = 633 nm, a maximum saturation magnetization 4πMs = 1255 Gauss with a minimum in-plane coercivity Hc = 35 Oe, and the narrowest full width at half maximum FWHM = 0.06° of the (444) Bragg reflection rocking curve. The analog of the Verdet constant V = øF / 4πMs, also found to be dependent on the oxygen ambient pressure, reaches the value as high as 1.4 deg/νm-kG at 633 nm, suggesting that this material is useful for MO applications.

Ce-substituted YIG films grown by pulsed laser deposition for magneto-optic waveguide devices

Ce-substituted yttrium iron garnet films have been epitaxially grown on [111]-oriented gadolinium gallium garnet substrates by pulsed laser deposition technique. X-ray diffraction measurements show epitaxial growth of the garnet film along its [111] axis. The films were grown at substrate temperature of 790/spl deg/C and various oxygen partial pressure varying from 10 to 100 mTorr. From the magnetic properties measured by VSM, we found that the fabricated (CeY/sub 2/)Fe/sub 5/O/sub 12/ films have in-plane magnetization with no preferential easy direction in the plane. The saturation Faraday rotation values obtained from measurements at /spl lambda/=633 nm and room temperature are found to be dependent on the oxygen pressure, with the maximum value of 0.7 deg//spl mu/m for the films grown at 50 mTorr.

Integrated optical isolator based on efficient nonreciprocal radiation mode conversion

An integrated optical isolator is demonstrated based on efficient nonreciprocal conversion from a fundamental TM mode to a deep TE radiation mode away from the cutoff. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet, which has a very large Faraday rotation. 27 dB isolation is obtained at a wavelength of 1535 nm.

Integrated Nonreciprocal Devices for Application in Optical Communication Systems

AbstractWe describe our recently developed integrated isolators. Their structure is simple, in that it consists solely of a single-mode channel magneto-optic waveguide. The operating principle is that a backward fundamental TM mode wave is converted to higher-order or radiation TE modes while a forward fundamental TM mode wave propagates with no mode conversion. These isolators are realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. We obtain 13-27 dB isolation around a wavelength of 1.55 μm. We also review our recent study on a hybrid-integrated polarization-independent optical circulator based on a nonreciprocal Mach-Zehnder interferometer which does not need a polarization-beam splitter. We obtain 14.1-23.7 dB isolation at λ = 1.55 μm.

Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy

Ce-substituted yttrium iron garnet films are epitaxially grown in situ on (111)-oriented substrates of Gd3Sc2Ga3O12 garnet by conventional rf diode sputtering for application to magneto-optic waveguide devices in optical communication systems. The lattice constant of the substrates is larger than that of the previously used (Gd,Ca)3(Ga,Mg,Zr)5O12 garnet substrates whose lattice constant is smaller than that of the films. The lowest ever reported propagation losses of 9.7 dB/cm in the TE mode and 5.8 dB/cm in the TM mode are obtained for a film thickness of 0.5 μm at λ=1.55 μm.

Preparation of Ce-Substituted Yttrium Iron Garnet Films for Magneto-Optic Waveguide Devices

Ce-substituted yttrium iron garnet films are epitaxially grown in situ on (111)-oriented substrates of (Gd, Ca, Mg)3(Ga, Zr)5O12 garnet by conventional rf diode sputtering for application to magneto-optic waveguide devices in optical communication systems. Pure argon or argon containing a small amount of oxygen is used as the sputter gas. After sputtering, the films are annealed in a nitrogen atmosphere. By optimizing this process, film propagation loss can be reduced while maintaining a large Faraday rotation. A propagation loss of 13 dB/cm and a Faraday rotation of -3900°/ cm have been obtained at a wavelength of 1.55 µ m.

Crystallinity of Ce Substituted YIG Films Prepared by RF Sputtering

The crystallinity of Ce-substituted yttrium iron garnet ( Ce1\\colonYIG) film was studied by measuring X-ray diffraction (XRD) and deformation and by transmission electron microscope (TEM) observation. The Ce1\\colonYIG films were prepared on anisotropic etched or unetched GGG and cation doped GGG (GCGMZG) substrates by RF sputtering. They have a narrow crystallization region as regards substrate temperature and this region becomes narrower as the O2 gas flow rate is increased. The XRD measurements and TEM observation revealed that crystallized Ce1\\colonYIG films have a multilayered structure except for those on GCGMZG substrates. Their layered structure was dependent on their thickness, the substrate treatment, the lattice constant difference between the film and the substrate and the O2 flow rate. They also exhibited compressive deformation which originated mainly from the lattice constant difference between the film and the substrate. The crystal growth mechanism of Ce1\\colonYIG films was considered on the basis of recent work on the growth mechanism of compressively deformed strained semiconductor film.

Integrated optical isolator based on nonreciprocal higher-order mode conversion

An integrated optical isolator based on nonreciprocal conversion from a fundamental TM mode to a higher-order TE mode is proposed and experimentally demonstrated. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. 24 dB isolation is obtained at a wavelength of 1550 nm.

Optical waveguide isolator based on nonreciprocal radiation

A new waveguide isolator which has a simple structure is proposed and experimentally demonstrated. The isolator operates on the basis of nonreciprocal guided-radiation mode conversion in a channel magneto-optic waveguide. The isolator was realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. 13.3 dB isolation was obtained at a wavelength near 1.55 μm.

Quantum theory of the strong magneto-optical effect of Ce-substituted yttrium iron garnet.

Calculations of the Faraday rotation (FR) and ellipticity spectra in the wavelength region between 360 and 1260 nm caused by the ${\mathrm{Ce}}^{3+}$ ions in the Ce-substituted yttrium iron garnets based on the quantum theory are presented. The calculation of the temperature dependence of FR at 633 and 1150 nm wavelengths is presented as well. The Faraday effect contributed by the ${\mathrm{Ce}}^{3+}$ ions is caused mainly by the intraionic electrical dipole transitions between the 4f and 5d configurations. The effect of the crystal field (CF), superexchange interaction, and spin-orbit coupling on the magneto-optical (MO) effect has been discussed. The energy differences between the lowest and second CF-split 5d levels and the lowest CF-split 4f level are 1.36 and 3.10 eV, respectively. Therefore there are anomalous rotatory dispersions at about 1.36 and 3.10 eV. The difference of the transition intensity for the right- and left-handed circularly polarized light between the lowest CF-split 5d level and the ground state is negative, while the corresponding value for the transition between the second CF-split 5d level and the ground state is positive. So the FR is positive over the whole photon energy region between 1.36 and 3.10 eV and is negative outside this region. Since the energy differences between the CF splitting levels of the excited configuration are comparable with the energy difference between the mean energies of the excited and ground configurations, the MO coefficient varies with temperature. The admixing of different multiplets of the ground configuration is another cause which makes the MO coefficient vary with temperature.