Bi-substituted Rare-earth Iron Garnet Research Articles

Magneto-optical property and magnetic anisotropy of (100) oriented R0.5Bi2.5Fe5O12 (R = Eu, Sm, and Pr) thin films prepared by metal–organic decomposition

Bi-substituted rare-earth iron garnets, R3−xBixFe5O12 (Bi:RIG), where R represents one of the rare-earth elements, exhibit the excellent magneto-optical (MO) properties that increase with Bi content x. In addition, magnetic properties of Bi:RIGs, such as the magnetization, the magnetic anisotropy, and the magnetostriction, could be controlled by choosing rare-earth elements. In this paper, we report on R0.5Bi2.5Fe5O12 (Bi2.5:RIG, R = Pr, Sm, and Eu) thin films on Gd3Ga5O12 (GGG) (100) single crystal substrates prepared by the metal–organic decomposition method. XRD analysis reveals that Bi2.5:RIG thin films are grown along the same orientation with GGG substrates, and their lattice constants are dependent on the ionic radii of the rare-earth ions. MO measurements show that Faraday spectra of the Bi2.5:RIG thin films have a typical spectral structure observed for Bi:RIGs. The magnetic anisotropy constants, the uniaxial magnetic anisotropy energy Ku, and the magnetocrystalline anisotropy energy K1 of Bi2.5:RIG (R = Y, Pr, Nd, Sm, and Eu) thin films are investigated by using the ferromagnetic resonance measurement.

Optical determination of the exchange stiffness constant in an iron garnet

Brillouin light scattering measurements were performed in the backscattering geometry on a Bi-substituted rare earth iron garnet. We observed two different peaks: One is attributed to a surface spin wave in the dipole-exchange regime while the other is referred to as a backscattering magnon mode, because the incident light in this case was scattered backward by exchange-dominated spin wave inside the material. We propose a method to estimate the exchange stiffness constant from the frequency of the backscattering magnon mode. The obtained value is comparable with the previously reported values for Y3Fe5O12.

Faraday Rotation Spectra Analysis on TbYbBiIG Crystals in Optical Communication Band

his paper is concerned with the FR spectra analysis on the Bi, Tb and Yb partially substituted iron garnet crystals of Tb3-x-yYbyBixFe5O12. A specific FR (-1617o/cm at 1.55μm), a low FWC (0.009%/nm at 25oC) of Tb0.91Yb1.38Bi0.71Fe5O12 crystals grown from Bi2O3 self-fluxed melts can be used as broadband optical communication components. In order to interpret their FR spectra, a theory based on molecular-orbital levels of Fe3+ in tetrahedral and octahedral sites is used. It is shown that in the case of higher Bi3+ substitution, FR is mainly determined by the contribution of Fe3+ in the octahedral site. Furthermore, two types of rare-earth ions (Tb3+ and Yb3+) moderate the contribution to FR from Fe3+ in octahedral and decahedral sites and eventually have caused that Bi-substituted mixed rare-earth iron garnet has a near-zero Faraday rotation wavelength coefficient (FWC).

Growth and Characterization of (TbBiGaIG) Film/(TbYbBiIG) Crystal Composite

Bi-substituted rare-earth iron garnet Tb2.40Bi0.60Ga0.13Fe4.87O12 (TbBiGaIG) films on magnetic rare-earth iron garnet Tb0.87Yb1.60Bi0.53Fe5O12 (TbYbBiIG) substrates were grown by a liquid phase epitaxy (LPE) technique. The microstructure and magneto-optical properties of TbBiGaIG film/TbYbBiIG crystal composite were investigated. The (110)-oriented TbBiGaIG single crystal film was epitaxially grown on the TbYbBiIG substrate. The TbBiGaIG film/TbYbBiIG crystal composite showed an improved temperature dependence of Faraday rotation because of the compensation effect.

Faraday rotation spectra analysis of Bi-substituted mixed rare-earth iron garnet crystals in optical communication band

Through combining two types of Bi-substituted rare-earth iron garnet crystals with opposite Faraday rotation wavelength coefficient (FWC) signs, the Bi-substituted mixed rare-earth iron garnet (Tb3−x−yYbyBixFe5O12) crystals with low FWC are used in optical isolators for broadband optical communication. However, the Faraday rotation (FR) spectra of bismuth-substituted mixed rare-earth iron garnet crystals have not yet been theoretically studied in the optical communication band [wavelength (λ)=1.5–1.62μm]. In order to interpret their FR spectra, a theory based on molecular-orbital levels of Fe3+ in tetrahedral (d) and octahedral (a) sites is used. It is shown that in the case of higher Bi3+ substitution, FR depends mainly on the contributions of Fe3+ in the octahedral sites. Furthermore, two types of rare-earth ions (Tb3+ and Yb3+) moderate the contributions to FR from Fe3+ in octahedral and decahedral sites and eventually have caused that Tb3−x−yYbyBixFe5O12 crystals has a near-zero FWC.

Development of a prototype laser magneto-optical imaging system

In order to detect the dynamic motion of local magnetic fluxes inhigh-TC superconductor devices, we are developing a new type of magneto-optic sensor with ahigh sensitivity and ultrafast response. For this purpose, we have fabricated aprototype laser magneto-optical detection system and evaluated its performance. Inthe setup, we prepared Bi-substituted rare earth iron garnet films as a Faradayindicator using the metal organic decomposition method. By using this prototypesystem, we succeeded in observing the magnetic field distribution around aYBa2Cu3O7−δ strip line applied with a bias current, and also succeeded in detecting the small magneticfield induced by a bias current as small as about 10 mA.

A compounded rare-earth iron garnet single crystal exhibiting stable Faraday rotation against wavelength and temperature variation in the 1.55 μm band

The Bi, Tb and Yb partially substituted iron garnet bulk single crystals of Tb 3− x − y Yb y Bi x Fe 5O 12 were grown by using Bi 2O 3/B 2O 3 as flux and accelerated crucible rotation technique for single-crystal growth. Faraday rotation (FR) spectra showed that the specific FR of the (Tb 0.91Yb 1.38Bi 0.71)Fe 5O 12 crystal under magnetic field at saturation was measured to be about −1617°/cm at λ=1.55 μm, Faraday rotation wavelength coefficient (FWC, 0.009%/nm) in the wavelength range of 1.50–1.62 μm and Faraday rotation temperature coefficient (FTC, 3.92×10 −5/K) at λ=1.55 μm were even smaller than that of YIG. It is proven that through combining two types of Bi-substituted rare-earth iron garnets with opposite FWC and FTC signs, the compound rare-earth iron garnets with low FWC and FTC may be obtained due to the compensation effect. The saturation magnetization of (Tb 0.91Yb 1.38Bi 0.71) Fe 5O 12 crystal is 0.48×10 6 A/M and is also much smaller than that of YIG. We have found empirically that there is a simple relationship between the FR θ f( x) and Bi content x for Tb 3− x − y Yb y Bi x Fe 5O 12, which is given by θ f( x)=(−2759 x+400)°/cm.

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.

Magneto-Optical Properties of Bi-Substituted Rare-Earth Iron Garnets in 1.55-µm-Wavelength Band

Bi-substituted rare-earth iron garnets, (REBi)3Fe5O12 (REBiIG), are used in wide-band optical communication as Faraday rotators in an optical isolator. However, the influence of rare-earth ions on the magneto optical (MO) properties of REBiIG crystals, such as specific Faraday rotation (FR) and coercive force, is not clear. The aim of the present work is to compare the MO properties of garnets doped with different rare-earth ions. REBiIG (RE=Ho, Yb, or/and Tb) crystals were grown from Bi2O3 self-fluxed melts by the top-seeded solution growth method under the same conditions. It was found that both specific FR and coercive force decrease with an increase in rare-earth ion radius. The FR wavelength stability of HoYbBiIG is better than that of YbBiIG but worse than that of HoBiIG. However, the FR temperature stability of HoYbBiIG is worse than that of YbBiIG but better than that of HoBiIG. It is noted that HoYbBiIG crystal is a trade-off between HoBiIG and YbBiIG crystals in terms of MO properties.

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.

10 GHz-Class Magneto-Optic Field Sensing with Bi-Substituted Rare-Earth Ion Garnet Rotation Magnetization Employed

We have experimentally investigated RF sensitivity and frequency response of the rotation magnetization (RM) based Faraday effect in a Bi-substituted rare-earth iron garnet plate, with the aim of exploring the possible implementation of an optical instrument for wideband magnetic field probing. We have pointed out and confirmed experimentally the effectiveness of applying an in-plane static magnetic field for the sensitivity enhancement of RM signal detection; the signal-to-noise ratio was improved by 40 dB or more. The RM frequency response is flat within a fluctuation of 2.5 dB from 10 MHz up to 3 GHz and its 3 dB bandwidth is as broad as 14 GHz. We have also proposed fiber-edge magneto-optic probe head structures which may provide the frequency response and sensitivity mentioned above.

Magneto-optic properties and sensing performance of garnet YbBi:YIG

A co-doped Bi-substituted rare-earth iron garnet single crystal YbBi:YIG was grown from high temperature solution, and was used first time for magneto-optic optical fiber current sensors. The crystal has the specific Faraday rotation angle −404° cm −1, magneto-optic figure of merit 25.8° dB −1, saturation magnetic field 1400 Oe, and temperature coefficient 4.2×10 −4 K −1 (at room temperature, λ=1.55 μm). It has larger Faraday rotation angle and magneto-optic figure of merit and lower temperature sensibility than pure YIG. A laboratory prototype sensor was established using the YbBi:YIG crystal as Faraday rotator element, and its sensing performance was tested under a 50 Hz factory frequency current. The tested results showed that the sensor system had high accuracy, sensitivity and good linearity.

A New Bi-substituted Rare-earth Iron Garnet for a Wideband and Temperature-stabilized Optical Isolator

A wideband and temperature-stabilized optical isolator for 1.55-μm wavelength was developed using a new Bi-substituted holmium–ytterbium ion garnet (HoYbBiIG) single crystal as a Faraday rotator. The optical isolator features 0.34-μm bandwidth, less 0.6 dB insertion loss and over 37 dB backward loss at a wavelength of (1.55 ± 0.17) μm throughout the temperature range from −10 to 60 °C. The Faraday rotation and optical absorption loss of HoYbBiIG were investigated in the near-infrared wavelength region (λ = 0.9 to 1.7 μm). The specific Faraday rotation of Ho0.85Yb1.02Bi1.13Fe5O12 is about −767°/cm at λ = 1.55 μm. The Faraday rotation wavelength and temperature characteristics of HoYbBiIG crystals are also discussed. These results indicate that the Bi-substituted holmium–ytterbium iron garnet single crystals realize a high Faraday rotation stability against temperature and wavelength in the near-infrared region.

光方式磁界センサの高精度化

We developed highly accurate optical magnetic field sensors. The sensor optical system has a confocal optical system using ball lenses. Bi-substituted rare earth iron garnets were prepared by the LPE method for use as Faraday rotators. We found that a new garnet composition, Bi1.14Gd0.57La0.02Y1.27Fe4.53Ga0.47O12, showed stable temperature characteristics of the sensitivity; The temperature dependence of the sensor output was less than 2.0% from -20°C to +80°C. We also improved the linearity error in the small magnetic field by using the film thickness dependence of the wall coercive force. The linearity error of the sensor output was within 1.0% for alternating magnetic fields from 3.0 Oe to 420 Oe. The sensors achieved high performance with regard to the linearity and the temperature characteristics.

BI-DYIG FILMS : ANALYSIS OF THE DY CONTRIBUTION TO THE FARADAY ROTATION.

At λ= 633 nm, very accurate measurements of the Faraday rotation on epitaxial garnet films of the composition {R3-xBix}[Fe2](Fe3)O12 with R = Dy, Y and high Bi content (x ≅ 1.30) are reported, in the temperature range 10 -620 K under magnetic field up to 20 kOe applied along the [111] direction. The analysis of the data in terms of the sublattice magnetization reveals, at low temperatures, a large contribution of the rare earth {c } sublattice induced by the Bi substitution. This enhancement of the electric dipole Faraday rotation is strongly temperature dependent and vanishes at room temperature. This result is compared with that observed for the same Bi-substituted rare earth iron garnets in the near infra-red band.

Optical magnetic field sensors with high linearity using Bi-substituted rare earth iron garnets

Optical magnetic field sensors with high linearity were developed. Bi-substituted rare earth iron garnets were prepared using the liquid phase epitaxy method for use as the Faraday rotators of the sensors. The linearity error of the sensor output was obtained within 1.0% for alternating magnetic fields of up to 300 Oe. The sensor optical system has a new converged beam optical system using ball lenses. The linearity of these sensors is much better than that of sensors using a collimated beam optical system with graded index lenses. Sensors using the collimated beam optical system are nonlinear, since only the zeroth-order beam diffracted by the garnet maze domains is detected. Sensors using the converged beam optical system have high linearity because of the detection of diffracted beams up to the second-order. The experimental results agreed well with the calculated results.

光方式磁界センサの直線性改良

Optical magnetic field sensors with high linearity and low harmonic distortion were developed. Bi-substituted rare earth iron garnets were prepared by the LPE method for use as the Faraday rotators of these sensors. The linearity error of the sensor output was obtained within ±1.0% for alternating magnetic fields of up to 300 Oe. The sensor optical system has a new converged beam optical system using ball lenses. The linearity of these sensors is very much better than that of sensors using a collimated beam optical system, on account of the use of graded index (GRIN) lenses. Sensors using GRIN lenses have non-linearity, since only the zeroth-order beam diffracted by garnet maze domains is detected. Sensors using ball lenses have high linearity bacause of the detection of diffracted beams up to the second-order. These experimental results agree well with the calculated results.

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.

Optical isolators using Bi-substituted rare-earth iron garnet films

Using Bi-substituted rare-earth iron garnet film, (GdBi)3 (FeAlGa)5O12 or (YbTbBi)3 Fe5O12, grown by liquid phase epitaxy technique, we have fabricated a compact, low cost and high performance optical isolator for near-infrared wavelength region, in comparison with conventional isolator using yttrium iron garnet (YIG) single crystal as Faraday rotator. Typical insertion loss and isolation of developed isolators are 0.6 dB and 35 dB respectively at λ=1.31 μm and the size is 6ϕ×6 mm. The isolators, which could be used in the wavelength range of 1.31 to 1.55 μm, are also fabricated with insertion loss of less than 1.1 dB and isolation of more than 35 dB.