Bi-substituted Iron Garnet Films Research Articles

Wavelength and temperature characteristics of BiYbIG film/YIG crystal composite structure for magneto-optical applications

We report the wavelength and temperature characteristics of novel Bi-substituted rare-earth iron garnet films grown on a YIG substrate by a modified liquid phase epitaxy (LPE) technique. The Faraday-rotation spectrum was measured by the magneto-optically modulated dual-frequency technique with the wavelength varied from 800 nm to 1700 nm. The resultant Bi0.37Yb2.63Fe5O12 (BiYbIG) LPE film/YIG crystal structure showed an increased Faraday-rotation coefficient due to Bi3+-ion doping on the dodecahedral sites of the iron garnet without increasing absorption loss; therefore, a good magneto-optical figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved (21.5 deg/dB and 30.2 deg/dB at 1300-nm and 1550-nm wavelengths, respectively, at room temperature). In addition, since the Yb3+ and Y3+ ions provide opposite contributions to the wavelength and temperature characteristics of the Faraday rotation, the resultant BiYbIG LPE film/YIG crystal structure showed a flat Faraday-rotation curve versus wavelength and temperature. The Faraday-rotation wavelength coefficient was reduced to 0.06 %/nm at 1550-nm wavelength. The Faraday-rotation temperature derivative was reduced to 0.006 deg/°C at 1300-nm wavelength and 0.007 deg/°C at 1550-nm wavelength, respectively.

Ion Beam Sputter-Fabrication of Bi–YIG Films for Magnetic Photonic Applications

We report the fabrication of polycrystalline and epitaxial Bi-substituted yttrium gallium iron garnet films on amorphous oxide coated Si wafers and single crystalline gadolinium gallium garnet (GGG) substrates for potential magnetic photonic device applications via reactive ion beam sputtering of a single phase (Bi/sub 0.8/Y/sub 2.2/)(Ga/sub 1/Fe/sub 4/)O/sub 12/ target. The observed Bi-YIG film magnetic properties are sensitive to sputtering parameters like the reactive molecular oxygen ion or radical neutral oxygen atom flux substrate impingement, and the specular or nonspecular geometry control of the reflected neutral substrate bombardment. Nonferrimagnetic amorphous Bi-YIG films are obtained using the specular sputtering geometry that can be recrystallized as randomly oriented single-phase YIG films with in-plane anisotropy using post-deposition rapid thermal annealing (RTA). Also, nonspecularly sputtered Bi-YIG films with improved interfaces and weak nanocrystallinity can be fabricated, yielding "as grown" ferrimagnetic behavior that can be further improved by RTA. Epitaxial Bi-YIG films on GGG with extremely soft magnetic characteristics and strong in-plane anisotropy have also been fabricated.

Liquid phase epitaxy growth of bismuth-substituted yttrium iron garnet thin films for magneto-optical applications

The novel Bi-substituted rare-earth iron garnet films were grown by the modified liquid phase epitaxy (LPE) technique for use as a 45° Faraday rotator in optical isolators. First, single crystals of Y 3Fe 5O 12 (YIG), with a lattice constant of 1.2378 nm, were grown by means of the Czochralski method. Using the seed crystal of YIG instead of the conventional non-magnetic garnet of Gd 3Ga 5O 12 as a substrate, a film of BiYbIG was grown by means of the LPE method from Bi 2O 3–B 2O 3 fluxes. The structural, magnetic and magneto-optical properties of BiYbIG LPE film/YIG crystal composite have been investigated using directional X-ray diffraction, electron probe microanalysis, vibrating sample magnetometer and near-infrared transmission spectrometry. The saturation magnetization 4πM s has been estimated to be approximately 1200 G. The Faraday rotation spectrum was measured by the method of rotating analyzer ellipsometry with the wavelength varying from 800 to 1700 nm. The resultant Bi 0.37Yb 2.63Fe 5O 12 LPE film/YIG crystal composite showed an increased Faraday rotation coefficient due to doping Bi 3+ ions on the dodecahedral sites of the magnetic garnet without increasing absorption loss, therefore a good magneto-optic figure of merit, defined by the ratio of Faraday rotation and optical absorption loss, has been achieved of 21.5 deg/dB and 30.2 deg/dB at 1300 nm and 1550 nm wavelengths, respectively, at room temperature. Since Yb 3+ ions and Y 3+ ions provide the opposite contributes to the wideband and temperature characteristic of Faraday rotation, the values of Faraday rotation wavelength and temperature coefficients were reduced to 0.06%/nm and 0.007 deg/°C at 1550 nm wavelength, respectively.

Fabrication and characterization of Bi-substituted yttrium iron garnet films by pulsed laser deposition

We have systematically investigated the effects of processing parameters, including various oxygen pressures (Po2) ranging from 200 to 1000 m Torr and substrate temperatures (Ts) ranging from 500 to 750°C, on the characteristics of Bi-substituted yttrium iron garnet (Bi:YIG) films grown on (111) gadolinium gallium gamet (GGG) substrates. Bi: YIG films were grown using a pulsed laser deposition method with an ArF excimer laser (λ=193 nm). Although the compositions of all the Bi:YIG films grown at the constant Ts of 600°C were close to the target composition irrespective of Po2, the Bi contents were slightly increased with increasing Po2, which was consistent with the variation in Faraday rotation angles (θF). In addition, the crystallinity of the Bi:YIG films was deteriorated with increasing Po2, and their grains became irregular. At Ts above 700°C, Bi-deficient yttrium iron garnet films were grown. Consequently, high quality epitaxial Bi:YIG films exhibiting Faraday rotation angles of −1.0≈−1.5 degree/μm were successfully grown at the substrate temperatures in the range of 500–650°C when the Po2 of 200 mTorr was used.

Spin-wave resonances in a nonuniform bilayer iron-garnet film

Magnetic resonances are investigated in bilayer Bi-substituted iron garnet films, one layer of which possesses easy-axis and the other easy-plane anisotropy. The behavior of resonances as a function of film thickness, temperature, and annealing is studied. It is shown experimentally that the resonance absorption lines observed in such a nonuniform structure in an external magnetic field oriented perpendicular to the film plane correspond to ferromagnetic (FMR) and spin-wave (SWR) resonances. In addition, the SWR series is excited in the most nonuniform part of the film. A qualitative model explaining the experimental data and making it possible to obtain experimentally the profile of the effective-magnetic-anisotropy field throughout the thickness of the film is proposed.

Non-equilibrium garnet films grown by pulsed laser deposition

Bi-substituted gadolinium iron garnet films were deposited on GGG(111) and NGG(111) substrates by irradiating KrF excimer laser on to targets with the composition Bi x Gd 3− x Fe 5O 12 (0≤ x≤3) at a substrate temperature of 580620 °C. Analyses on structure, composition and angle of Faraday rotation, θ F, were carried out. From these measurements, it is confirmed that a thermally non-equilibrium phase has grown when the amount of substituted bismuth, x, exceed 2.

A theoretical analysis of magneto-optical Faraday effect of YIG films with random multilayer structures

The magneto-optical (MO) Faraday effect of Bi-substituted yttrium iron garnet (Bi:YIG) films with random multilayer structures is analyzed using the random matrix approach, and the Faraday rotation angles (θF) are examined in comparison with those of periodic multilayer films. The films consist of Bi:YIG films and SiO2 dielectric films, which are stacked randomly (periodically) so as to form the random (periodic) multilayer structures. Similarly to the case of MO Kerr effect, a considerable enhancement in θF takes place when the film structure meets the nonreflection condition of light. In particular, θF of the film reaches a maximum of 1.4°/μm at λ=1.15 μm, with the fraction of Bi:YIG layers in the random multilayer film is 41%. This value is about seven times larger than that of a single Bi:YIG film (θF=0.2°/μm), and cannot be attained with periodic multilayer films.

Bi-substituted iron garnet films exhibiting stable Faraday rotation against wavelength variation in the 1.55 μm band

We found a Bi-substituted iron garnet film (Tb/sub 1.86/Bi/sub 1.14/Fe/sub 4.67/Al/sub 0.24/Co/sub 0.09/O/sub 12/) which was characterized by stable Faraday rotation against wavelength variation in the 1.55 /spl mu/m band. First, Co- and Bi-substituted iron garnet films were grown by liquid phase epitaxy (LPE), and the dependence of their Faraday rotation against wavelength variation was measured. It was found that the dependence of Bi-substituted iron garnet films on wavelength was reduced in the 1.55 /spl mu/m band due to a Faraday rotation attributable to Co/sup 3+/ ions. Faraday rotation-wavelength coefficients (FWC) of these films in the 1.53 /spl mu/m-1.57 /spl mu/m band were 0.01%/nm, or virtually zero. Also relations between FWC and film composition were discussed.

Magneto-Optical Faraday Effect of YIG Films with Random Multilayer Structures

Magneto-optical Faraday effect of Bi-substituted yttrium iron garnet (Bi:YIG) films with random multilayer structures was analyzed by using the random matrix approach. It was found that the random multilayer structure is very effective for enhancing the Faraday effect of the Bi:YIG film, which is much superior than that of the periodic multilayer films.

The effects of substrate temperature and oxygen pressure on pulsed laser deposited Bi-substituted Dy iron garnet films

Polycrystalline thin films of highly Bi substituted Dy iron garnets, [(BixDy3−x(Fe, Ga)5O12], with [111] crystalline orientation perpendicular to the film plane were grown on (111) Gd3Ga5O12, single crystal substrates using pulsed laser deposition technique. In the deposited films, Bi stoichiometry was found to be very sensitive to both substrate temperature and oxygen pressure. The Bi volatilisation problem was relieved by depositing in a high background pressure of oxygen. The results demonstrated that high quality garnet films with large magneto-optical (MO) effects and square hysteresis loops could be obtained when the substrate temperature did not exceed 590°C and the oxygen pressure was kept in the neighbourhood of 0.2 mbar. The MO behaviour of these films compared well with predictions based on the fundamental constants of Bi substituted Yttrium Iron Garnet thick films, grown by liquid phase epitaxy. The coercivity could be varied from a few hundred Oe to several kOe by controlling the oxygen pressure and film thickness.

Laser ablation of Bi-substituted gadolinium iron garnet films

Bi-substituted gadolinium iron garnet films were deposited by laser ablation. The composition, the structure and the magnetic properties of the films were found to be strongly dependent both on the compositions of the targets and on the pressure of oxygen. The highest values of Bi-substitution up to x = 1.44 with uniform composition were obtained, after annealing in air.

Reducing the optical absorption of LPE garnet films at a wavelength of around 1000 nm

This paper concerns the reduction of optical absorption loss L of Bi-substituted rare-earth iron garnet films at a wavelength of around 1000 nm for use as a 45/spl deg/ Faraday rotator of an optical isolator. First, a single crystal of Nd/sub 1.21/Gd/sub 1.74/Sc/sub 2.07/Ga/sub 2.98/O/sub 12/, with a lattice constant of 1.2619 nm, was grown by the Czochralski method. Using this crystal as a substrate, Nd/sub 1.69/Bi/sub 1.31/Fe/sub 5/O/sub 12/ film was grown by the LPE (Liquid Phase Epitaxial) method. The resultant LPE film showed a reduced optical absorption at around 1000 nm, because its optical absorption peak at around 900 nm due to the Fe/sup 3+/ crystal field transition from /sup 8/A/sub 1g/ to /sup 4/T/sub 1g/ shifted toward short wavelengths. In addition, the LPE film's Faraday rotation coefficient increased, since Nd, as Bi does, contributes negatively to the Faraday rotation. The value of L for the LPE film was found to be 2.6 dB at a wavelength of 980 nm, and 1.0 dB at 1017 nm.

Magneto-Optical Characteristics of Bi-Substituted Rare-Earth Iron Garnet Films Prepared by Laser Ablation

Bismuth substituted rare-earth iron garnet (Bi:RIG) films were prepared on (111) gadolinium gallium garnet (GGG) and glass substrates b laser ablation using the ArF excimer laser. Crystal structure of the garnet phase was obtained above the substrate temperature of about 500° C on GGG substrate without postdeposition annealing and on glass substrate with postdeposition rapid thermal annealing. Films with the easy magnetization axis normal to the film plane were obtained for Bi:DyIG and Ga- or Al-substituted Bi-YIG on GGG substrate. The Faraday hyster- esis loops and the magnetic domain were observed. On the other hand, the easy magnetization axis normal to the film plane was obtained for Bi:DyIG films on the glass substrate with postdeposition rapid thermal annealing.

Nonstoichiometric Properties of Bi-Substituted Yttrium Iron Garnet Sputtered Films

Structural, magnetic and magnetooptical properties of nonstoichiometric Bi-substituted yttrium iron garnet (Bi-YIG) films have been studied in terms of Fe concentration. The garnet films were prepared by rf sputtering using targets which had various Fe contents. In the wide range of Fe content from about 3.9 to 5.4, garnet phases were obtained at an annealing temperature of 650° C. For the Fe contents ranging from 1.9 to 5.1, saturation magnetization increased linearly, and beyond the Fe content of 5.1, it dropped sharply. By considering the magnitude of Faraday rotation of the garnet phase formed in the films (θ F/M s) and Curie temperature, it is expected that the Bi concentration in the garnet-phase crystallites in the prepared films increases as Fe content increases. It was observed, in energy dispersive X-ray spectrometry (EDX) and secondary ion mass spectrometry (SIMS) analyses, that the excess Bi ions in low-Fe-content films concentrated at the surface, near the film-substrate interface, at the edge of the films and at grain boundaries.

Magnetic and magneto-optical properties of Bi-substituted garnet films

Crystallized Bi-substituted iron garnet films were deposited by rf sputtering and pyrolysis methods. The effects of the substitution of some rare-earth elements (Dy, Ho) and nonmagnetic elements (Ga, Al) were investigated. Adaptive substitution can improve the performance of garnet films for magneto-optical recording. The effect of doping with Cu on the coercive force H c is discussed, and optimum design of a practical disk with a bilayer structure is presented. The calculation of the temperature profile in the medium by thermal writing is given. Some results of static read-write experiment are reported.

Observation of Flux Density Distribution in YBa2Cu3Ox Superconductor Thin Film Using Bi-Substituted Iron Garnet Film

Bi-substituted iron garnet film with a large Faraday rotation and perpendicular magnetization was prepared, and the film domain patterns were used to observe the flux penetrating superconducting YBa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> thin films. Observations were performed for both square and disk-shaped YBa <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Cu <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> films. The penetration behavior depends on defects and the shape of the film. We confirmed that the flux density in superconducting film as observed through the iron garnet film domain patterns was nearly the same as that estimated from the sample magnetization.

Completely Bi-Substituted Iron Garnet (BIG) Films Prepared by Electron Cyclotron Resonance (ECR) Sputtering

Completely Bi-substituted iron garnet (BIG) films were epitaxially synthesized on garnet substrates by electron cyclotron resonance (ECR) sputtering. The critical temperature for the epitaxial growth, crystallinities, and Faraday rotation θF of BIG films depend on the O2 gas flow rate. With an optimum flow rate of 7 sccm, single-crystal BIG films were obtained at temperatures above 390°C, and θF achieved its largest value of 8.4×104 deg/cm (λ=0.633 µm). The minimum ferromagnetic resonance (FMR) linewidth ΔH was 70 Oe; this is the smallest value ever reported. The uniaxial perpendicular magnetic anisotropy is mainly caused by the elastic deformation induced by the thermal expansion mismatch between the film and the substrate.

Magnetic garnet films prepared by ion beam sputtering and their application to optical isolators

As a 45 degrees Faraday rotator of an optical isolator in the visible region, highly Bi-substituted iron garnet films prepared by reactive ion beam sputtering-deposition (RIBS) are investigated. Both Bi/sub 3/Fe/sub 5/O/sub 12/ and Bi/sub 2.5/Y/sub 0.5/Fe/sub 5/O/sub 12/ films are deposited onto

Effects of Cu Addition on Bi-Substituted Garnet Film for Magnetooptical Recording

Polycrystalline Bi-substituted iron garnet films with Cu added were prepared on glass substrate by rf diode sputtering followed by annealing. The addition of 3.4 at% Cu was effective both for decreasing the size of crystallites to about 1 μm, and for increasing the coercivity to 5.4 kOe. The shape of statically recorded bits was also improved.

Synthesis of ferromagnetic Bi-substituted yttrium iron garnet films by laser ablation

Bismuth-substituted yttrium iron garnet (Bi:YIG) films were deposited on gadolinium gallium garnet substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Bi-substituted YIG films by laser ablation. Films have a garnet single phase above the substrate temperature of 490 °C, and the film composition does not deviate largely from the target composition and it is almost constant in the temperature range between 490 and 580 °C. The saturation magnetization of the film is 1500 G at room temperature. Faraday rotation angle θF at a wavelength of 830 nm at room temperature is −0.3×104 °/cm.