Bi-substituted Iron Research Articles

Bi-Directional Faraday Rotation Selective Enhancement on Embedded Nano-Gratings

The magneto-optic rotation enhanced by plamonic resonance brought a new method in the research of magnetoplasmon and magneto-optical devices. To further the availability of this method, the Faraday effect on embedded nano-gratings with Bi-substituted yttrium iron garnet substrate is investigated here to achieve bi-directional rotation enhancement selectively. The surface of the simulation structure is designed as 1-D gratings to excite extraordinary optical transmission, and the transmitted light is rotated in the magneto-optic (MO) material. It is found that the characteristic of the bi-directional Faraday rotation enhancement can be greatly influenced by the embedding depth of the metal strips in the MO material. According to this, without changing the applied magnetic field or turning over the MO material, the selectively enhanced Faraday rotation is produced along two opposite directions. Moreover, by optimizing the thickness of metal, a great improvement of figure of merit is obtained. Finally, in the same wavelength regime, the properties of the structure are contrasted when the metal is set to be gold or silver, respectively. This letter provides a useful thought in magnetoplasmon studies, and can be used to fabricate many magneto-optical devices.

The Effect of Faraday Rotation Enhancement in Nanolayered Structures of Bi - Substituted Iron Garnets

The effect of considerable enhancement of Faraday rotation (FR) and figure of merit (Q) in Bi, Gd, Al-substituted iron garnets plus Bi2O3 (Bi, Gd, Al: YIG / Bi2O3) nanocomposite films on Gd3Ga5O12 (GGG) substrates was found. It reached threefold enhancement of the FR and twofold of the Q one. These films were produced by reactive ion beam sputtering of appropriate targets and following separate annealing. In addition it was determined that in double layer Bi-substituted yttrium iron garnet (Bi: YIG) nanostructures on GGG substrates the upper layer (0.5 – 3.0 nm) considerably affects the magneto-optical properties of the “thick” (8.0 – 10.0 nm) bottom layer. The possible reasons of these effects are discussed.

Evaluation of Nonlinear Effect in High Power Spin Pumping in Polycrystalline Bi-Substituted Yttrium Iron Garnet (Bi:YIG)/Pt Bilayer Structure

We have demonstrated a quantitative evaluation of spin pumping at uniform excitation in linear and nonlinear regimes of microwave absorption in a polycrystalline Bi-substituted yttrium iron garnet (Bi:YIG)/Pt bilayer structure. The evaluation is performed based on a ratio of magnitude of pumped spin currents to amplitude of uniform precession which are estimated from inverse spin Hall effect voltage and microwave absorption intensity at various incident powers. The ratio shows additional contribution to spin pumping by spin waves generated from uniform precession via nonlinear coupling between them. We have also clarified the additional contribution by the generated spin waves at various frequencies based on the ratio.

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.

Preparation and Magnetic Properties of Low Temperature Sintering Bi-Substituted Yttrium Iron Garnet

The low temperature sinterability and magnetic properties of Bi-substituted yttrium iron garnet (YIG) polycrystalline samples were studied in this paper. The results showed that Bi-substitution can lower garnet phase formation temperature from about 1200oC to 900oC and ceramic sintering temperature from over 1300oC to about 1050oC respectively. The Bi-substitution leads to a decrease in initial permeability and an increase in ferromagnetic resonance linewidth (ΔH) of sintered specimens. Saturation magnetization decreases and coercive force increases a few with an increase of Bi content. The mechanism of Bi-substitution on initial permeability and ΔH is discussed. The change in initial permeability of Bi-substituted specimens relative to unsubstituted YIG results from Bismuth volatilization and weakening of superexchange interaction. The lattice dilatation in Bi-substituted YIG gives cause for a decrease of saturation magnetization and an increase of coactivity force.

High Saturation Induction for Bi-Substituted Yttrium Iron Garnet Prepared Via Sol Gel Technique

Y3.0-xBixFe5O12 samples (x = 0.2 and 0.4) were prepared via novel sol-gel and conventional solid-state techniques. The effect of bismuth in both techniques was investigated in terms of shrinkage, density, hysteresis and initial permeability. Sharp and clear diffraction XRD lines with highest peak appear at about 32° of the 2I¸, for all the powders sintered at 900°C and 1250°C for both techniques. In evaluating the magnetic properties, it was observed that the saturation induction (1.1902kG) of sample prepared via sol-gel technique (Y2.8Bi0.2Fe5O12) is more than 200% higher than sample with the same formula prepared via conventional technique. Fine grained microstructure with average grain size of about 5I¼ m and higher shrinkage, about 11% were observed from the samples prepared via sol gel technique. It is concluded that samples prepared via sol gel technique appear to be an attractive route due to the possible reduction of cost of production and the enhanced magnetic and structural properties of the sample.

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.

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.

Magnetooptical property of sodium borosilicate gel-glass containing Bi-YIG fine particles

Composite materials which consist of ferro- or ferrimagnetic fine particles in a glass matrix are expected to have a large residual magnetization and coercive force because of their fine magnetic domain structure, and has potential for superior magneto-optical properties compared with single or polycrystalline materials. In this study, the sodium borosilicate (NBS) glass containing Bi-substituted yttrium iron garnet (BixY3−xFe5O12: BiYIG) fine particles, which show a superior magneto-optical effect, was prepared by the sol-gel method. BiYIG fine particles were stable in NBS gel-glass matrix during densification because the sintering temperature (580°C) of NBS gel was low enough to avoid pyrolysis of BiYIG and the reaction between BiYIG fine particles and the matrix. The Faraday rotation angle spectrum of the composite after deducting the contribution of the NBS glass matrix was intermediate between the reported ones of YIG and Bi0.25YIG polycrystalline thin films. The change of the Faraday rotation angles of the composite with imposing magnetic field showed a hysteresis loop. It was in good agreement with that of the magnetization curve of the composite.

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.

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.

Bi-substituted rare-earth iron garnet composite film with temperature independent Faraday rotation for optical isolators

(BiLuGd)IG/(BiGd)(FeGa)G composite films of which the temperature derivatives of Faraday rotation angle at 45 degree ( \equiv\beta ) are nearly zero, were grown by a two-step liquid phase epitaxial (LPE) method. The relative intensity noise (RIN) of the 1.3 μm laser diode (LD) with an optical isolator using the β=0.00 deg/°C garnet composite film were measured in comparison with an isolator using the garnet crystal with β of 0.05 deg/ °C. The relation between the RIN and the feedback light power and the relation between the RIN and β value were clarified. It was found that the increase of the RIN by periodic noise caused by feedback light to the LD from the fiber-far-end was observed when the feedback light power increases more than -62dB. In the practical temperature range of -20\sim+60\deg C garnet composite films with β=0.00 deg/°C are required in order to prevent the periodic noise.

Magneto-Optical Properties of (GdBi)3(FeAl)5O12 Bulk Single Crystals and Their Application to a 1.3 ¿m Optical Isolator

A compact optical isolator has been developed for use at a wavelength of 1.3 μm, using a Bi-substituted gadolinium iron garnet (Gd3-xBixFe5O12) single crystal as a Faraday rotator. The optical isolator features a 0.35 dB insertion loss, 34 dB backward loss, and approximately 33.6 dB isolation ratio at 1.3 μm. The insertion loss and the magneto-optical figure of merit in Gd1·8Bi1·2Fe5O12 at 1.3 μ are about 0.025 dB and 3000 deg/dB, respectively. The temperature and magnetic field dependences of the Faraday rotation and the optical absorption have been measured for Gd3-xBixFe5-yAlyO12 single crystals, grown by an improved flux method in which Bi2O3 is used as a flux. The saturation field of the Faraday rotation decreases with Al substitution. The magneto-optical figure of merit of the Fe3+ absorption region at about 0.9 μm was approximately independent of the Al content for y ≪ 0.5. The Faraday rotation in Gd3-xBixFe5O12 (0.85 ≪ x ≪ 1.2) changes by about 7.5%/50°C as the temperature rises above 25°C.

Magneto-Optics: Its Past and Present

A very brief survey is made of the research conducted on magneto-optics in recent years. A highly Bi-substituted rare earth iron garnet is described as a candidate magneto-optical material. PtMnSb, representing a new type of metallic magneto-optical material, is grown in thin film form for use in magneto-optical recording media. Semi-magnetic semiconductors such as CdMnTe are also new candidates for uses in other areas. Applications as magneto-optical device elements in various areas of optoelectronics also show great promise.

Magneto-optical property of Bi-substituted yttrium Iron garnet films on SmGG substrates in a wavelength region of 0.7-0.9 µm

Highly Bi-substituted yttrium iron garnet films grown epitaxially on SmGG substrates are investigated for compositions of (BiY) 3 Fe 5 O 12 , (BiY) 3 - (FeAl) 5 O 12 and (BiGdY) 3 (FeAl) 5 O 12 . A specific rotation of 7670 deg/cm and an optical absorption of 180 cm-1at 0.8 μm are obtained for a (BiGdY) 3 (FeAl) 5 O 12 film. These values give the figure of merit 10 deg/dB. Growth of thick films, saturation fields of the films and the optical reflection are investigated.