Rare-earth Iron Garnet Research Articles

Nonlinear optics of gyrotropic media: second harmonic generation in rare-earth iron garnets

Second harmonic generation in nonlinear gyrotropic media in the form of epitaxial films of rare-earth iron garnets was investigated for the first time both experimentally and theoretically. The anisotropy of the process in a magnetic field, as well as the Faraday and Kerr effects were studied. In the nonlinear interaction case the Faraday effect was half that in the linear case. An expression was obtained for describing the Faraday and Kerr effects for the case of a nonlinear interaction involving a semiinfinite nonlinear gyrotropic medium and a nonlinear gyrotropic layer: a characteristic feature of these effects was a nonlinear coordinate dependence. The experimentally observed characteristics of the two effects were explained by a model allowing solely for the linear magnetooptic parameters of the medium. Possible mechanisms of the appearance of the nonlinearity in iron garnets in a magnetic field were analyzed.

Magneto-optical recording on garnet films

As next generation magneto-optical (MO) recording media, rare earth iron garnet films with the magnetization aligned perpendicular to the film surface are prepared by sputtering and pyrolysis on glass substrates. Compared to the current amorphous metal MO films the garnet films are high in corrosion resistance and strong in MO effect, especially when enhanced by Bi 3+ or Ce 3+ which substitutes for the rare earths. However, garnet films on glass substrates are obtained only in polycrystalline form, which causes an important problem yet to be fully solved, the problem of media noise generated at grain boundaries.

Enhancement of Faraday rotation in a fibre Fabry-Perot cavity

The enhancement of Faraday rotation in a rare-earth iron garnet plate inside a fibre Fabry-Perot resonator is demonstrated. An enhancement factor of seven is obtained with a resonator finesse of 10.

Cation distribution and IR spectra of rare-earth gallium iron garnets

The Mössbauer and IR measurements of the R3Fe5-z Gaz O12 garnets, where R = Lu, Yb, Er, Y, Gd, Sm and 0 ⩽ z ⩽ 5, indicate a tendency of decreasing tetrahedral site preference of Ga with increasing size of the dodecahedral cation.

Effect of melt composition on Bi incorporation in iron garnets

The saturation temperature, the growth rate and the crystal composition of rare-earth iron garnet films grown from a PbOBi 2O 3B 2O 3 flux were investigated. The concentrations of the garnet component oxides, the proportions of the flux oxides, B 2O 3 and Bi 2O 3, and the ratio Fe 2O 3/RE 2O 3 in the melt were systematically varied to determine their effect. The melts generally obey Van Erk's theory of solubility and growth rate. However, an increase of either the B or Bi concentration in the melt linearly decreases the rare earth activity, which results in an increase in both the garnet solubility and the effective segregation coefficient of Bi into growing garnet films. Using the rare earth activity calculated from solubility data, a Bi segregation coefficient of 0.0010 is observed that is independent of melt composition and growth temperature.

Growth-induced magnetic and optic anisotropy in bismuth-substituted iron garnet films

The growth-induced uniaxial magnetic anisotropy constant Kgu and the growth-induced birefringence Δng of (111) oriented epitaxial iron garnet films of composition R3−xBixFe5−yAlyO12 with R=Y, Gd, Sm have been investigated as a function of supercooling temperature ΔTs. The uniaxial anisotropy constant Kgu increases linearly with increasing ΔTs (0≤ΔTs≤100 K) in agreement with results reported for other bismuth-substituted rare-earth iron garnets. Δng turns out to be a linear function of Kgu and ΔTs. Δng is independent of the rare-earth species R in contrast to Kgu. The optical anisotropy arises primarily from the iron ions on the octahedral and tetrahedral sites as could be shown by the strong influence of diamagnetic dilution of the iron sublattices in the garnet crystal.

Analysis of Magneto-Optic Readout with Circular Polarized Light

This paper presents a new design for magneto-optical pickups which detect the phase shift of circularly polarized light instead of the rotation of plane-polarized light. The use of a polarizing beam splitter and a quarter-wave plate enables a theoretical efficiency of 100%. Efficiency is important not only in order to reduce the laser power when recording, but also to avoid reflected light which would interfere with the laser output. We discuss the theory of readout from circularly polarized light and describe an experiment on reading from a rare earth-iron garnet magneto-optical disk. In conclusion, we discuss the advantages and drawbacks of such a reading method.

Thermal expansion of gallium garnets and Bi-substituted iron garnet epitaxial thick films

Abstract Lattice constants and thermal expansion of several Bi-substituted rare-earth iron garnet epitaxial films (Bi-RIG; R=Gd, Dy, Yb+Tb) and Ca, Mg and Zr-doped and undoped gadolinium gallium garnet substrates (CaMgZr-GGG and GGG) were measured in the temperature range 300 to 1073 K. In the measurements on the films, the substrates have been removed to render the films free from strain. While CaMgZr-GGG exhibits thermal expansion similar to that of GGG, Bi-substitution in the RIG films increases their thermal expansion. Therefore, when the Bi-RIG films are lattice-matched to the CaMgZr-GGG substrates at room temperature, the lattice mismatch at the growth temperature, 1073 K, amounts to 0.1–0.2%.

Temperature dependence of Faraday rotation in Bi-substituted terbium iron garnet films

The role of Tb3+ in the Faraday rotation θF of (Bi,Lu)-substituted terbium iron garnet Tb3−x−yLuyBixIG (x=0–1.1, y=0–0.9) films is studied. The temperature dependence of θF at λ=633 nm is measured in the temperature range of 10–600 K and the saturation magnetization 4πMs is measured in the temperature range of 4.2–450 K to clarify the contribution of the dodecahedral Tb3+. The temperature dependence of θF is analyzed by using two different models based on the three sublattice magnetizations. It is found that in the model where the Fe3+ contributions to θF in Bi-substituted iron garnet are assumed to be the same in all rare-earth iron garnets, the contribution of the Tb3+ site to θF is increased by Bi substitution. The variations of the Tb3+ coefficients with Bi content and temperature are also presented and discussed.

Overview of magneto-optic isolator materials and devices (invited) (abstract)

Recent research and developments on magneto-optic materials and devices using nonreciprocal properties are described. Investigations on the growth of Bi-substituted iron garnet bulk crystals and LPE-grown thin films are extensively carried out, and high quality and compact isolators for near-infrared wavelengths are realized. Temperature coefficient of the angle of Faraday rotation is decreased enough by using a combination of Bi and rare-earth ions substituted in these host garnets. These materials are also used as magneto-optic switches and magnetic field (current) sensors. Basic research on waveguide-type of magneto-optic devices is another subject. It is shown that growth-induced birefringence found in LPE-grown Bi–rare-earth iron garnet films is effective to achieve phase matching between TE and TM modes in a planar waveguide. The author would like to summarize some other subjects on magneto-optic recording materials being done at many research laboratories.

Faraday rotator materials for lasers (invited) (abstract)

Materials exhibiting strong Faraday rotation are of interest for components in laser systems. These include optical isolators, circulars, modulators, and switches in sizes ranging from microdevices for integrated optics to 30-cm-diam rotators for Nd:glass lasers used in inertial confinement fusion research. Properties of diamagnetic, paramagnetic, ferromagnetic, dilute magnetic semiconductors and free carrier rotators have been evaluated for various laser applications and for operation in the spectral range from the infrared to the ultraviolet and at various temperatures. Both crystalline and amorphous materials are considered; forms include bulk materials, fibers, and thin films. The characteristics of selected materials, including bismuth-substituted rare-earth iron garnets, Cd1−xMnxTe, and rare-earth doped glasses and crystals, are discussed. Relative figures of merit based on specific rotation, losses, cost, and special properties such as the nonlinear refractive index are also given.

A new improved (YbTbBi)/sub 3/Fe/sub 5/O/sub 12/ epitaxial thick film

The Faraday rotation coefficient of a (YbTbBi)/sub 3/Fe/sub 5/O/sub 12/ thick films grown by liquid phase epitaxy (LPE) on a (CaGd)/sub 3/(MgZrGa)/sub 5/O/sub 12/ substrate was found to be -2400 and -1600 deg/cm at lambda =1.31 and 1.55 mu m, respectively. This is believed to be the largest Faraday rotation coefficient exhibited by an LPE-grown thick film of Bi-substituted rare-earth iron garnets for Faraday rotators in practical use. The thickness required to achieve 45 degrees rotation was only 190 mu m for lambda =1.31 mu m and 290 mu m for lambda =1.55 mu m. The film could be successfully grown to about 300 mu m without crack formation. The Faraday rotator using this material has a low insertion loss, 0.3 dB for lambda =1.31 mu m and 0.2 dB for lambda =1.55 mu m, and isolation of about 40 dB. >

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.

Magnetic polaritons in an anisotropic film on a ferromagnetic substrate

Substituted rare-earth iron garnet thin films grown by liquid-phase epitaxy on rare-earth iron garnet and exhibiting low saturation magnetization with a uniaxial magnetic anisotropy in a direction perpendicular to the film surface have recently been reported. We have obtained the dispersion relations of surface and guided magnetic polaritons in the film-substrate composite system in the Voigt geometry including retardation effect. Two windows were obtained for the magnetic polariton modes, one corresponding to a surface mode and the other to a guided mode in the anisotropic magnetic film. For low value of the external magnetic field, the frequency of the guided mode moves down with increasing magnetic field while the frequency of the surface mode moves up. For a suitable choice of physical parameters now available in substituted iron garnet films, we predict a crossover of these two branches.

Magneto-optical properties of Bi-substituted epitaxial rare-earth iron garnet thick films

Films of (Yb,Tb,Bi)3Fe5O12 show excellent characteristics of the Faraday rotator at the wavelength of 1.3 μm; the rotation is −1800 deg/cm, insertion loss 0.3 dB, isolation 38 dB, and the temperature dependence of the Faraday rotation is 0.060 deg/K at room temperature. The films are grown epitaxially on the (Gd,Ca)3(Ga,Mg,Zr)5O12 substrates, from the melt in the flux PbO/B2O3/Bi2O3. The melt contains rare-earth ions (R=Y,Gd,Er,Dy,Tm,Yb,Lu) as c-site components of rare-earth iron garnets, and Fe and Ga+Al as a- and d-site components. The obtained film thickness is in the range 300–400 μm without appreciable defects on the substrate, with a 2-in. diameter. This technology will lead to the efficient production of the optical isolator used in optical systems.

Mixed rare-earth iron garnet (TbY)IG for magnetic field sensors

Temperature dependence of sensitivity constants, corresponding to Verdet constant, of dodecahedrally substituted (TbxY1−x)IG crystals grown by a conventional flux method and liquid-phase epitaxy method are studied. By measuring the variation of the sensitivity constant with temperature, it was found that crystals with X=0.19 show a minimum value of ±1% between 300 and 400 K. The temperature dependence of sensitivity constants on Tb concentration was explained by a simple theoretical calculation.

Preparation of GdIG:Bi Single Crystals by Crucible Rotation Flux Method

GdIG single crystals with Bi substituted were grown by the crucible rotation flux method to reduce the optical absorption loss in the near infrared range. This loss is a serious problem with rare earth iron garnets used for optical isolators. The grown crystals have extremely few carriers, and the resistances are in the range 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Ω-cm as compared with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Ω-cm for crystals prepared by the conventional technique. It is thought that the oxygen defects, ie, amount of resultant Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , in the GdIG:Bi single crystals grown by this method will be significantly lower than that in similar crystals prepared by the conventional method. The optical absorption loss was one third that of the optical loss in crystals grown by the conventional flux method.

GROWTH-INDUCED BIREFRINGENCE IN LPE-GROWN IRON GARNET FILMS

The optical birefringence of various LPE-grown rare-earth and Bi-substituted iron garnet films are studied. In addition to the stress-induced birefringence, it is shown that there exists growth-induced birefringence ΔnfG in the films containing light rare-earth or Bi ions. In Bi garnet films the ΔnfG disappears on annealing and the thermal behavior of ΔnfG is similar to that of the growth-induced uniaxial magnetic anisotropy constant KuG. Furthermore, the BiG content dependence of ΔnfG is similar to that of KuG. As a result, it is suggested that the ΔnfG and KuG originate in the same microscopic structure which is of an anisotropic character. It is pointed out that the positive sign and the magnitude of ΔnfG in Bi garnet films are effective for the phase matching between TE and TM modes in a planar waveguide.

MAGNETOOPTICAL ROTATION OF PrIG AND NdIG

Bulk single crystals and epitaxial films of Pr3Fe5O12 and Nd3Fe5O12 have recently been grown for the first time by Fratello et al. Magnetooptical (Faraday) rotation of these two compositions has been measured at room temperature over the wavelength range 0.5 to 2.5 μm. Of all the pure rare earth iron garnets, only the rotation of Pr3Fe5O12 approaches that of the Bi containing garnets now being used in magnetooptical devices.

High-TC Superconducting Oxide Films Produced from Solution Precursors

ABSTRACTSuperconducting films of Ba2RECu3O7−x were prepared from aqueous and aqueous-alcoholic mixed solutions of barium, rare earth (RE), and copper nitrates. The solutions were sprayed onto heated (100) orientated MgO, ZrO2 —9%Y2O3 and SrTiO3 substrates to form a dehydrated nitrate precursor; subsequent thermal treatment yielded the superconducting 2:1:3 compound. Earlier magnetic film studies with aqueous-alcoholic mixed solutions of rare-earth iron garnet precursors showed that alcohol improves the spreading and drying of solutions on substrates. Here, however, alcohol significantly lowers the solubility of Ba(NO3)2. Some compositions tend to phase segregate during film preparation. A key objective of this study was to understand reaction paths of the precursors in order to optimize the furnace annealing schedule. Film and substrate reactions complicate the process, especially for SrTiO3, which otherwise has a good lattice match with films. Analytical methods used were Knudsen effusion mass spectrometry, thermogravimetric analysis, x-ray diffraction, secondary ion mass spectroscopy, electron microscopy and temperature-dependent resistivity. The best samples showed a Tc of 95K and had zero resistivity below 89K. Advantages of this process include: simplicity of equipment, short deposition time; ease of making composition adjustments; and possible deposition on complex shapes.