Bismuth-substituted Yttrium Iron Garnet Films Research Articles

Extraordinary enhancement of magneto-optical Faraday rotation angle in Bi-YIG/Pt/glass prepared by metal organic decomposition method

We achieve the extraordinary enhancement of magneto-optical Faraday rotation angle for bismuth-substituted yttrium iron garnet (Bi-YIG) using the metal-organic decomposition method, by introducing a Pt underlayer. The Faraday rotation angle reaches -25°/μm for the sample with a Pt thickness of 45 nm, which is 5 times higher than that of a bare thin film, setting a new record value for chemically synthesized Bi-YIG films. Through X-ray diffractometer, vibrating sample magnetometer, and energy dispersive X-ray spectroscopy analyses, we found that this enhancement is attributed to improved crystallinity, saturation magnetization, and the formation of a PtBi alloy phase, facilitated by Pt acting as an absorbing layer of Bi. We propose that the Bi-YIG/Pt film structure, with an optimum thickness of Pt underlayer, shows great promise for applications in various magneto-optical devices that require high detection sensitivity for small signals.

Praseodymium-dopant effect on bismuth-substituted yttrium iron garnet films on fused silica glass substrate at the 1310 and 1550-nm wavelengths

The optical and magneto-optic (MO) properties of the praseodymium (Pr)-dopant effect on bismuth-substituted yttrium iron garnet (Bi:YIG) films coated on fused silica glass substrates by using the metal-organic-decomposition (MOD) method with chemical solutions were investigated at the 1310 and 1550-nm wavelength regions. The maximum Faraday rotation angle of the Pr-codoped Bi:YIG (Pr,By:YIG) film was observed to be 0.09 and 0.046 deg/μm at the wavelengths of 1310 and 1550 nm, respectively, when the film was annealed at a temperature of 750 °C, while those of the plain Bi:YIG film were 0.059 and 0.039 deg/μm. More than 50% improvement in the Faraday rotation value of the Pr,Bi:YIG film was observed compared to that of the Bi:YIG film at the 1310 nm wavelength. The absorption coefficient of the Pr,Bi:YIG film was comparable to that of the Bi:YIG film. Therefore, the Pr,Bi:YIG film prepared with the MOD method is potentially useful for MO applications such as optical isolators and circulators.

Concept of the Optomagnonic Logic Operation

We present the concept of the optomagnonic logic gate, where interference of spin waves excited by femtosecond laser pulses at multiple points by the inverse Faraday effect in a bismuth-substituted yttrium iron garnet film plays a decisive role. The resulting spin-wave distribution is determined by constructive and destructive interference, which is controlled by the polarization of laser sources. A variable platform with a spatial light modulator is used to control the overall spin-wave distribution by manipulating the arrangement of the local spin-wave sources. We demonstrate the experimental optical excitation of backwards volume magnetostatic spin waves at multiple points and use wavelet analysis and micromagnetic numeric simulations to analyze them. Simulations provide an excellent agreement with the experimental data and are further used to model the magnon logical gate (xnor) based on optically excited spin-wave interference.

Broadband Enhancement of Faraday Effect Using Magnetoplasmonic Metasurfaces

Magnetooptical Faraday effect enables ultrafast photonic devices based on nonreciprocal polarization rotation; however, the intrinsic weakness of Faraday effect prevents miniaturization and practical applications of nonreciprocal photonic devices. Magnetoplasmonics offers new mechanisms for enhancing magnetooptical effects using surface plasmon resonances, which generally have narrow bandwidths. Using finite-difference time-domain modeling, we demonstrate a magnetoplasmonic metasurface, which remarkably enhances the Faraday effect in a wide spectral range. While Faraday rotation in a bare bismuth-substituted yttrium iron garnet film is below 0.02° in the studied range of 600–1600 nm, the proposed metasurface yields few degrees of rotation in a broad band with a maximum exceeding 6.5°, which indicates about three orders of magnitude enhancement. We also show that by optimizing the configuration of the system including the geometry and excitation parameters, the metasurface response and operation band can be tuned further, and rotation values higher than 20° can be achieved. Finally, we present guidelines for designing magnetoplasmonic metasurfaces.

Mode conversion characteristics of multimode magneto-optical Bragg diffraction cells

We study the dependence of magneto-optical (MO) coupling coefficients on the modal fields for the design of multi-mode MO Bragg cells. The mode conversion and diffraction efficiencies between the same order TM and TE modes can theoretically be up to about 98% by adjusting the excitation frequency of the fundamental-mode magneto-static forward volume wave (MSFVW) in the bismuth-substituted yttrium iron garnet film at the optimized thickness and length. The different order mode conversion is also available by means of the higher-mode MSFVWs. The resulting mode conversion-based switch function is discussed.

Magneto-optical properties of spin-coated bismuth-substituted yttrium iron garnet films on silicon substrates at 1550-nm wavelength

Bismuth-substituted yttrium iron garnet (Bi:YIG) films were prepared by using spin coating processes with metal-organic-decomposition-method-based solutions on crystalline silicon (Si) substrates, and their magneto-optic properties at the 1550-nm wavelength region were investigated by performing various thermal treatments. The maximum Verdet constant of the Bi1Y2Fe5O12 film on the Si substrate with a middle buffer layer of Bi2Y1 Fe5 O12 was measured to be 1 072 038°/T/m at 1550-nm wavelength in the unsaturated linear magnetization region by accounting for the negative Verdet constant of the silicon substrate. The optimum thermal treatment condition was observed at the maximum annealing temperature of 700 °C and the annealing speed of 3 °C/min. These spin coating enabled processes may be included to the conventional complementary metal-oxide semiconductor fabrication processes to demonstrate integrated optical waveguide-type isolators on silicon-on-insulator wafers.

Near-field mechanism of the enhanced broadband magneto-optical activity of hybrid Au loaded Bi:YIG.

We unravel the underlying near-field mechanism of the enhancement of the magneto-optical activity of bismuth-substituted yttrium iron garnet films (Bi:YIG) loaded with gold nanoparticles. The experimental results show that the embedded gold nanoparticles lead to a broadband enhancement of the magneto-optical activity with respect to the activity of the bare Bi:YIG films. Full vectorial near- and far-field simulations demonstrate that this broadband enhancement is the result of a magneto-optically enabled cross-talking of orthogonal localized plasmon resonances. Our results pave the way to the on-demand design of the magneto-optical properties of hybrid magneto-plasmonic circuitry.

Spectrometer based real-time magnetic Faraday rotation spectroscopy of Bi-YIG thin films

Abstract In this work, we have investigated the bismuth-substituted yttrium iron garnet (Bi-YIG) thin films prepared on glass substrate by modified metal-organic decomposition method. Real-time Faraday rotation spectrometer was used to characterize the magneto-optical properties of Bi-YIG films. The reliability of the measurement system and optimized analyzer setup was confirmed by comparing the Jones matrix calculations and measured results. The effect of annealing condition on the structural, magnetic and magneto-optical properties was investigated. A clear garnet-phase without secondary phase was observed for the Bi-YIG films annealed above 800 °C. Faraday rotation spectra of these films reveal the correlation between their crystallinity and magneto-optical properties. The highest Faraday rotation angle of −3.1 °/μm was achieved for 800 °C annealed sample. Simultaneous evaluation of real-time Faraday rotation spectra and the corresponding hysteresis loops can establish a path for the application of time-resolved magneto-optical spectroscopic analysis of magnetic thin films.

RGB Magnetophotonic Crystals for High-contrast Magnetooptical Spatial Light Modulators

Magnetooptical spatial light modulators (MOSLMs) are photonic devices that encode information in photonic waveforms by changing their amplitude and phase using magnetooptical Faraday or Kerr rotation. Despite the progress on both MO materials and switching methods, significant improvements on materials engineering and SLM design are needed for demonstrating low-power, multicolor, analog and high-contrast MOSLM devices. In this study, we present design rules and example designs for a high-contrast and large figure-of-merit MOSLM using three-color magnetophotonic crystals (MPC). We demonstrate for the first time, a three-defect MPC capable of simultaneously enhancing Faraday rotation, and high-contrast modulation at three fundamental wavelengths of red, green and blue (RGB) within the same pixel. We show using 2D finite-difference time-domain simulations that bismuth-substituted yttrium iron garnet films are promising for low-loss and high Faraday rotation MOSLM device in the visible band. Faraday rotation and loss spectra as well as figure-of-merit values are calculated for different magnetophotonic crystals of the form (H/L)p/(D/L)q/(H/L)p. After an optimization of layer thicknesses and MPC configuration, Faraday rotation values were found to be between 20–55° for losses below 20 dB in an overall thickness less than 1.5 µm including three submicron garnet defect layers. The experimental demonstration of our proposed 3-color MOSLM devices can enable bistable photonic projectors, holographic displays, indoor visible light communication devices, photonic beamforming for 5 G telecommunications and beyond.

Effects of heating rate on the magneto-optical properties of bismuth-substituted yttrium iron garnet films prepared via modified metal-organic decomposition

This work investigated the effects of heating rate and annealing on the magneto-optical properties of bismuth-substituted yttrium iron garnet (Bi-YIG) thin films on glass and (111)-oriented single-crystalline gadolinium gallium garnet (GGG) substrates fabricated by metal-organic decomposition (MOD). We modified the MOD method by eliminating the pre-annealing process. We performed annealing at various temperatures to determine the optimal temperature for obtaining the Bi-YIG phase. We then annealed at the optimized temperature using various heating rates. The optimal conditions were annealing for 1 h at 750 °C at a heating rate of 30 °C/min on GGG to obtain highly crystallized fine grains. The Faraday rotation for this film was about −10.5°/μm. The optimized heating rate enhanced the magneto-optical properties due to improved crystallinity and saturated magnetization. The Bi-YIG thin films prepared by this prescribed MOD method exhibited excellent magneto-optical performance and are potential candidates for applications in optical devices.

Effect of pre-crystallization on the preparation of thick Bi-YIG films by the metal–organic decomposition method

Bismuth-substituted yttrium iron garnet films with a thickness of about 0.8–1.2μm were fabricated on glass substrates by using a metal–organic decomposition method. We observed that thick samples fabricated by intermediate short time sintering (pre-crystallization process) showed enhanced magneto-optical properties, good crystallinity, and high saturation magnetization. For the sample prepared with the pre-crystallization process the Faraday rotation angle was measured to be −3.75°/μm which was larger compared to the thick film prepared without pre-crystallization. The lattice constant and the grain size of the film were about 12.45Å and 43.8nm, respectively.

Modification of Bi:YIG film properties by substrate surface ion pre-treatment

The effect of a controlled ion beam pre-treatment of (111)-oriented Gd3Ga5O12 substrates on the magneto-optical properties and surface morphology of the ultrathin bismuth-substituted yttrium–iron garnet films with a composition Bi2.8Y0.2Fe5O12 was studied. It has been shown that the observed sign inversion of magneto-optical effects (Faraday rotation and magnetic circular dichroism) observed in films that were deposited on the GGG substrate pre-treated by 1keV and 4keV Ar+ ion beams is a result of the substrate surface amorphization caused by the ion bombardment.

Electromagneto-Optical Scanning of the Magnetic Domains Local Areas of Bismuth-Substituted Yttrium Iron Garnets

Magneto-electric properties of the magnetic domains local areas of bismuth-substituted yttrium iron garnet films are investigated. The electromagneto-optical (EMO) scanning method was used in our experiments when probing by laser beam various sites of separate magnetic domains of the film. Registered in our experiments the nonlinear and linear components of EMO effect does not remain to constants at optical scanning of various points of the magnetic domain. I.e. the local EMOE picture from the separate sites of the domain must be more informative than an averaged one in the multidomain case.

Preparation of nanocrystalline bismuth-substituted yttrium iron garnet films with enhanced Faraday magneto-optical figure of merit by pyrolysis of coprecipitated hydroxide slurry

Nanocrystalline Bi-substituted yttrium iron garnet films have been prepared by coprecipitation titration, once-through coating of hydroxide slurry, and pyrolysis. The resulting films with grain sizes of 10–20 nm are fabricated at a pH value of 12 and heat treated of 700 °C for 1 h. At the incident light wavelength of 633 nm, the maximum special Faraday rotation of 3.6×10 4°/cm and Faraday magneto-optical figure of merit of 6.7°/dB were obtained. The influence of pH value and heat treatment on film grain size, crystallinity, and magneto-optical properties is demonstrated.

A gigahertz surface magneto-plasmon optical modulator

We propose a novel high-speed magnetooptic (MO) modulator based on the optical excitation of surface magneto-plasmon (SMP) waves in bismuth-substituted yttrium iron garnet (Bi-YIG). A model describing magnetization dynamics of the Bi-YIG film is used in conjunction with an SMP reflectivity model to evaluate the performance of the device. In developing the reflectivity model, the dispersion relation for the SMP waves at a Bi-YIG-metal interface is derived. The optical response of the device is modeled for various driving pulses, and the performance of the device is discussed in terms of response time, efficiency, and bandwidth. Using practical material parameters, it is found that the modulator has an improved efficiency over MO modulation devices relying on bulk propagation for comparable driving current pulse durations, as well as the added benefits of a miniature design, multigigahertz operation, and tunable bandwidth. The analysis presented here provides a useful framework for the design and development of magneto-plasmon photonic devices.

Parametrically driven first-order Suhl instability and nonlinearities in bismuth-substituted yttrium iron garnet films

We have demonstrated the enhancement of spin-wave nonlinearities in a bismuth-substituted yttrium iron garnet (Bi-YIG) film by parametrically exciting the first-order Suhl instability at the difference frequency of two simultaneous driving frequencies. The results show that parametric excitation of spin waves can cause this instability to grow at low threshold powers, which, in turn, channels power to other nonlinear spin-wave modes. Multiple interactions between spin waves lead to the enhancement of nonlinear processes.

Influence of surface plasmons on the Faraday effect in bismuth-substituted yttrium iron garnet films

The Kerr rotation and ellipticity of Bi1.8Y1.2Fe5O12 films (Bi:YIG) with the easy axis of magnetization perpendicular to the film plane was investigated in a Kretschmann setup at the wavelength 1.31 μm. The sample was coated by a thin Au film in order to excite plasmons at the free Au surface. An ellipsometric setup, supplemented with a magnetic field oriented perpendicularly to the film plane was used to measure the reflected p and s components of an incoming p polarized wave. The phase difference between the outgoing p and s waves was found by an indirect procedure. A minimum in Kerr rotation and a maximum in Kerr ellipticity could be observed at the surface plasmon resonance angle. Using the Berreman formalism, the experimental curves for the prism/Bi:YIG/Au system could be reproduced by bulk optical constants of the constituents. The asymmetry of the ellipticity curve is demonstrated to arise from a sudden variation in the phase. The effects of the field distribution and the surface roughness are discussed.

Ｂｉ置換ＹＩＧ膜を用いた１次元磁性フォトニック結晶の作製と特性

One-dimensional magnetophotonic crystals with bismuth-substituted yttrium iron garnet films were fabricated by a method that combines rf magnetron sputtering and pulsed-light annealing. The media exhibited significantly high transmittance and Faraday rotation at designated localized wavelengths of light in the photonic bandgap. These results coincide quantitatively with the theoretical prediction.

Magnetization and ferromagnetic resonance studies in implanted and crystal ion sliced bismuth-substituted yttrium iron garnet films

Bismuth-substituted yttrium iron garnet (Bi-YIG) is the material of choice in the fabrication of optical isolators. Recently some of us have demonstrated an ion-implantation based technique for detaching single-crystal Bi-YIG films from their gadolinium gallium garnet growth substrates, and for their subsequent bonding onto semiconductor wafers. In this article we study the magnetic properties of bubble-type Bi-YIG films with large out-of-plane uniaxial anisotropy in various stages of the separation process. We find that the implantation reduces the perpendicular anisotropy field from approximately 1435 to 750 Oe as a result of increased residual strain. Annealing partially restores the anisotropy to 900 Oe depending on annealing conditions. Chemical etching of the implanted sample separates the Bi-YIG film from the substrate at the sacrificial layer. Upon detachment the perpendicular anisotropy of the sample is nearly fully restored to its original value. The 9 GHz ferromagnetic resonance (FMR) linewidth of these films is large (440–520 Oe) and is only weakly affected by the processing.

Permanent magnet film magneto-optic waveguide isolator

Recent advances in high-coercivity planar-magnetization film magnets and Bi-YIG (bismuth-substituted yttrium iron garnet) film technology have opened up the possibility of fabricating very small magneto-optic devices. In this article we demonstrate that these two technologies can be brought together to fabricate a high performance waveguide magneto-optic isolator for use in integrated optical circuits. The device operates at 1.55-μm wavelength and consists of a waveguide etched into a Bi-YIG film whose magnetization is saturated by a 22-μm-thick TbCu7-type SmCo magnet with a coercivity of 4 kOe. Isolation ratios of 25 dB have been obtained in the wavelength region between 1490 and 1555 nm.