Iron Garnet Crystals Research Articles

Thermal Hysteresis of Photoinduced Magnetic Effect in Yttrium Iron Garnet

In single crystals of yttrium iron garnet irradiated with laser (the most effective wavelength is 700 nm) or white light at 77 K, a remarkable change of the temperature dependence of complex permeabilities μ' and μ is observed, which is peculiar to photoinduced magnetic effect. Simultaneously,conspicuous double peaks of DA around 125 K and 200 K below room temperature were found to be induced by light-irradiation, with correlative onset of the irreversible decrease of permeability insensitive to demagnetization at low temperature. In order to explain these observations, we propose a new model.

Thermal spike model applied to the irradiated yttrium iron garnet: Mean diffusion length of the energy deposited on the electrons

Single crystals of yttrium iron garnet Y 3Fe 5O 12 have been irradiated with 270 MeV 52Te, 760 MeV 86Kr and 1040 MeV 208Pb ions. The extent of the induced damage is determined using Rutherford backscattering spectrometry (RBS) in channeling geometry with a 2 MeV 4He beam. Taking into account these new results and the previous ones, the thermal spike model was applied to calculate track radii versus electronic stopping power for different beam energies using only one fitting parameter, λ the mean diffusion length of the energy deposited on the electrons by the slowing down of a swift heavy ion in the garnet. As the latent heat of fusion is unknown for yttrium garnet, the calculation was first performed by neglecting it. A λ value of (6.3±0.3) nm is extracted by fitting all the different results taking into account a velocity effect. Such a λ value is the high limit of the mean diffusion length since it decreases if the latent heat of fusion is not neglected. This value of λ is in agreement with the previous determinations made in the same conditions for resistant insulators, showing that λ should decrease when the band-gap energy increases.

Optical fiber current sensors using garnet crystal for power distribution fields

We introduce applied examples (already put to practical use) of power distribution fields of optical fiber current sensors using iron garnet crystal that have high sensitivity, high linearity and stable temperature characteristics. We also describe two types of new optical fiber current sensors developed recently aimed at cost reduction and high performance.

Thermal Hysteresis of Photoinduced Magnetic Effects in Yttrium Iron Garnet with a Small Amount of Oxygen Vacancy

In single crystals of yttrium iron garnet irradiated with white light at 77 K, a remarkable change was observed in the temperature dependence of complex permeabilities μ' and μ. Simultaneously, conspicuous double peaks of DA around 125 K (DA1) and 200 K (DA2) were found to be induced by the irradiation at 77 K, with correlative onset of an irreversible decrease of permeability at low temperature. Besides, the dark DA (DA3) independent of white-light irradiation was observed around the room temperature. The activation energy of DA (1, 2, 3) may be calculated as 0.46, 0.60, and 0.88 eV, respectively.

Growth of YIG and BiGdIG single crystals for magnetooptical applications

The study of gadolinium-bismuth iron garnet (GdBiIG) growth conditions led to a rough delimitation of the primary crystallization field of the garnet phase, with the following optimum composition of the melt (in mol%): 5.8 Gd2O3 + 34.1 Fe2O3 + 57.5 Bi2O3 + 2.6 V2O5. The addition of V2O5 is necessary to suppress crucible corrosion. A typical growth run in the range of 1370-940 K with a cooling rate of 1 K h−1 yields crystals of the mean composition Gd1.95Bi0.97Fe5.10O12. The slices with a final thickness of ≈ 0.3 mm, cut and polished from the crystals, showed the desired value of the Faraday rotation (FR) angle, 45 °. As an alternative, crystals of yttrium iron garnet (YIG) were grown by the top-seeding technique. Attention was devoted to making a detailed study of the temperature distribution in the melt and optimization of the forced stirring by the accelerated crucible rotation technique (ACRT). An extremely low cooling rate (0.1 K h−1) led to the growth of large crystals without inclusions. Cylindrical bars cut and polished from the YIG crystals showed the desired FR angle of 45 °.

Magnetic disaccommodation in single yttrium iron garnet crystal

Measurements of magnetic disaccommodation in single yttrium iron garnet (YIG) crystals are presented. Two peaks of 0.2%–0.3% are observed in the isochronal spectrum around 130 and 250 K. Comparison of our results with those on polycrystalline YIG samples and with similar data on illuminated and gamma ray irradiated single YIG crystal samples is provided.

A theoretical investigation on the magneto-optical spectra of Ce-substituted yttrium aluminium garnet

Calculations of the Faraday rotation and ellipticity spectra at photon energies between 1.6 and 4.0 eV (wavelengths between 775 and 310 nm) resulting from Ce3+ ions in Ce-substituted yttrium aluminium garnets (YAG:Ce) based on the quantum theory are presented. The Faraday effect contributed by the Ce3+ ions is caused mainly by the intra-ionic electrical dipole transitions between the 4f and 5d configurations. The Faraday effect of the Ce3+ ions in both the diamagnetic YAG and the ferrimagnetic yttrium iron garnet (YIG) crystals has a paramagnetic spectral shape but the resonance frequencies of YAG:Ce are at 2.76 and 3.7 eV, which are obviously higher than those of YIG:Ce. This difference can be explained by the fact that the crystal field acting upon the rare-earth ions in garnets depends strongly on the nature of the next-nearest neighbours. The differences between the transition intensities for the right- and left-handed circularly polarized light from both the lowest and the second crystal-field (CF)-split 5d levels to the ground state are negative. Therefore the Faraday rotation spectrum contributed by the Ce3+ ions in YAG has a wave-like shape in the energy region considered. However, for YIG:Ce, the difference between the transition intensities for the right- and left-handed circularly polarized light from the second CF-split 5d level to the ground state is positive. So the corresponding spectrum for YIG:Ce has a different shape. The calculated results are in good agreement with experiment.

High sensitivity fiber-optic magnetic field sensors based on iron garnets

Ferrimagnetic iron garnet crystals form the basis of magnetooptic magnetic field sensors which offer high sensitivity, broad-band frequency response, and compatibility with fiber optics. Recent developments at NIST promise still greater performance for these devices in the near term. Specifically, new designs for magnetic field sensors, electric current sensors, and novel experimental iron garnet compositions demonstrate the potential for significantly improving the performance of these devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Domain effects in Faraday effect sensors based on iron garnets

Domain-induced diffraction effects produced by two iron garnet thick films and two bulk crystals are compared. The thick films, characterized by a serpentine magnetic domain structure, produced nonlinear response functions; this is in qualitative agreement with a one-dimensional diffraction model. Bulk iron garnet crystals, which exhibited a complex three-dimensional domain structure, produced qualitatively similar effects that diminished with increasing crystal length. Differential signal processing resulted in a linear signal for the thick films and a primarily sinusoidal response for the bulk crystals.

Atomistic computer simulations of yttrium iron garnet as an approach to studying its defect chemistry: Extrinsic defects.

We report results of atomistic simulation studies concerning the incorporation of extrinsic defects in yttrium iron garnet crystals. We calculate defect formation energies in order to determine the most favorable impurity incorporation mechanisms in yttrium iron garnet.

Phenomenological description of spin-reorientational transitions in YIG:Si induced by linearly polarized light

Abstract The phenomenological description of induced anisotropy and photoinduced spin-reorientational transitions in magnetic crystals of yttrium iron garnet doped by Si is given. The phenomenological approach is based only on the most general crystal symmetry considerations. The theoretical results are in good agreement with the experimental data (Kovalenko et al., 1981).

Damage and conductivity of yttrium iron garnet irradiated with GeV-heavy ions

Single crystals of Si-doped yttrium iron garnet (YIG: Si) have been irradiated with 6 GeV 208Pb ions at 80 K and 300 K. The amorphization cross section, for a mean electronic stopping power of 35 MeV μm−1, was determined from the 300 K 57Fe Mössbauer spectra. When going from the crystalline to the amorphous phase, the 300 K dc conductivity was found to decrease versus fluence. This is interpreted by the lowering of the carrier mobility caused by disorder. Furthermore, the 300 K ac conductivity of amorphous YIG:Si exhibited above 10 kHz an ωα law, with α ⋍ 0.8, characteristic of hopping conduction. These results are discussed with respect to undoped YIG irradiated with GeV heavy ions. No significant effects neither of the irradiation temperature, nor of the electrical conductivity are observed on the damage cross section.

Novel bulk iron garnets for magneto-optic magnetic field sensing

We report measurements of the magneto-optic response function and frequency response for three bulk iron garnet crystals grown by a flux technique. The samples were the product of an intensive effort to develop iron garnet compositions with properties specifically optimized for magnetic field sensing. Sensitivity enhancement was achieved through both bismuth substitution (for increasing the saturation Faraday rotation) and gallium substitution (for reducing the saturation magnetization). One sample exhibited a value of magneto-optic sensitivity of 25/spl deg//mT for 1.3 /spl mu/m light. Frequency response measurements indicate that bismuth substitution actually improves performance (compared to unsubstituted yttrium iron garnet) in contrast with gallium, which causes substantial degradation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magneto-optic magnetic field sensors based on uniaxial iron garnet films in optical waveguide geometry

Iron garnet films which exhibit perpendicular uniaxial magnetic anisotropy are promising materials for magnetooptic magnetic field sensing. In an optical waveguide geometry, these materials exhibit large values of saturation Faraday rotation which in turn produce high sensitivity. The domain structure of these films favors magnetization rotation as the primary magnetization process. This process is significantly faster than domain wall motion, which is the primary magnetization process in bulk iron garnet crystals. Data which confirm the high sensitivity and wideband frequency response of these materials are presented. One film exhibits a virtually flat frequency response from DC to at least 1 GHz. Potential problems with waveguide sensors, such as birefringence and optical coupling efficiency appear to be soluble. >

Magneto-optic magnetic field sensor with 1.4 pT/√(Hz) minimum detectable field at 1 kHz

The Letter demonstrates that the sensitivity of magneto-optic magnetic field sensors employing iron garnets can be increased by approximately two orders of magnitude by applying flux concentration. A minimum detectable field of 1.4 pT/√(Hz) was measured when a cylindrical gallium-substituted yttrium iron garnet crystal was combined with two conically tapered nickel–zinc ferrite cylinders.

Magneto-optic characterization of iron garnet crystals using photoelastic modulation

Depolarization phenomena in demagnetized bulk iron garnet crystals are investigated with the aid of a photoelastic modulator. An experimental configuration which simultaneously measures Faraday rotation and depolarization as a function of applied magnetic field is described. The technique is demonstrated with samples of SF-57 glass, which exhibits no measurable depolarization, and bulk yttrium-iron-garnet, which shows pronounced depolarization in the demagnetized state.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Floating Zone Crystal Growth and Phase Equilibria: A Review

The thermal‐imaging floating zone technique can be used to grow crystals of yttrium iron garnet (Y3Fe5O12), aluminum‐doped yttrium orthoferrite (YFe0.88Al0.12O12), and magnetite (Fe3O4), which represent peritectic compounds, solid‐solution crystals, and atmosphere‐sensitive materials, respectively. The reactions involved in floating zone crystal growth are explained on the basis of phase diagrams. A review of crystal growth reports, including unpublished findings by the present authors, demonstrates how the crystallization processes, the reaction with the ambient atmosphere, and the composition variation in the obtained crystals can be explained or controlled on the basis of phase equilibrium. The floating zone technique is applicable to a variety of materials and remains a handy tool for materials research; however, its industrial application may be limited.

Boundary conditions of the transition from steady-state to unsteady-state regimes of free convection in high-temperature solutions of oxides. Single crystal growth in a steady-state regime

The transition from a steady-state to an unsteady-state regime of free convection under conditions imitating the conditions of oxide single crystal growth from high-temperature solutions has been investigated by physical simulation. A correlation characterizing the boundary conditions of this transition has been found. Indium and niobium doped single crystals of bismuth calcium vanadium iron garnet (Bi 3−2xCa 2xFe 5−xV xO 12) are grown in the presence of a steady-state flow of free convection in a high-temperature solution with PbO as a solvent. It is shown that at a commensurable growth rate this technique permits the growth of complex oxide crystals of a higher homogeneity than is the case of accelerated crucible rotation technique (ACRT) or the slow cooling technique.

Low-temperature anisotropy of the Faraday rotation in the samarium iron garnet

Faraday rotation (FR) measurements performed on single crystals of samarium iron garnet (SmIG) at 1.15-μ wavelength in a magnetic field up to 20 kOe applied along the 〈210〉 cubic direction in the 6–77-K temperature range are reported. Abrupt changes of both spontaneous FR and FR susceptibility are evidenced at 20 and 60 K, temperatures which correspond to the three spin-reorientation transitions 〈210〉■〈110〉■〈111〉; the results are compared to the FR data previously obtained for the 〈111〉 direction.

Magnetooptical Techniques in Self-Consistent Determination of Optical and Magnetooptical Constants of Magnetics

A method is presented which uses measurements of the angular relationships of the magnetooptical Kerr effects for a self-consistent determination of the optical and magnetooptical constants of magnetics. Any of the Kerr effects may be employed for this purpose. The method is tested in the areas of strong, moderate, and weak absorption on polycrystalline Ni films, orthoferrite yttrium and yttrium iron garnet crystals. The magnetooptical effects have some pronounced features in the weak absorption region at angles near the Brewster angle, where the effect behaviour is to a great extent determined by the properties of a thin transition layer which is located at the surface of the crystals. [Russian Text Ignored].