Ferrite Garnet Research Articles

Stability of artificial ferrite garnets with actinides and lanthanoids in water solutions

Extraction of the actinide-REE fraction and its subsequent incorporation into sparingly soluble crystalline phases (confinement matrices) is assumed in processing of spent nuclear fuel from high-level radioactive wastes (HLW). The chemical stability in the process of interaction with subsurface water governs the capability of a matrix phase to keep radionuclides from getting into the biosphere. In static experiments at 90 and 150°C, the chemical stability of ferrite garnets was investigated for three compositions with Th4+, Ce4+ and Gd3+ + serving as simulator components of the actinide fraction of HLW. Experiments were carried out in distilled water (pH 6.5), 0.01 M HCl solution (pH 2), and 0.01 M NaOH solution (pH 12). The behavior of ferrigarnet matrices depends on the acidity of the solution. In neutral and alkaline media, Th, Ce, and Gd are virtually not transferred into the liquid phase. Acid leaching promotes intense dissolution of garnet matrices. In this case, the leaching rate of Gd and Th from ceramics into the liquid phase is two orders of magnitude lower than the leaching rate of Ce because the Ce-doped phases contain less stable (relative to garnet) Ce-rich perovskite. Amorphization of the ferrigarnet structure due to 244Cm isotope decay leads to an increase in the leaching rate of Cm by no more than five times. In terms of radiation and chemical stability, ferrite garnets are not inferior to zirconolites and titanate pyrochlores. The experimental results suggest that garnet matrices can reliably immobilize actinides in subsurface repositories.

Formation of magnetic nanocrystals in germanate glasses doped with Fe and Dy

Magnetic nanocomposites were synthesized from germanate glasses doped with iron and dysprosium oxides at low concentrations. The formation of nanoparticles (∼5–20 nm in size) in glasses subjected to heat treatment under different conditions was observed using high-resolution electron microscopy. Nanoparticles had a well-resolved crystal structure. X-ray fluorescence microprobe analysis showed that iron and dysprosium are concentrated in particles. The examination of the field dependences of the magneto-optical effect revealed magnetic ordering in particles. A comparison of the interplanar distances obtained using electron microdiffraction with those of the known iron oxide compounds did not lead to unambiguous results. Almost all specific features in the magnetic circular dichroism spectra of the glasses corresponded to the features previously observed in the spectra of garnet ferrites. On this basis, it was assumed that the particles formed in the germanate glasses have a distorted garnet structure.

Influence of Implantation on the Magneto-Optical Properties of Garnet Surface

We have investigated the magneto-optical and optical properties of the ion implanted (YBiCaSmLu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (FeGeSi) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> garnet films. It has shown that the ion implantation influences significantly the magneto-optical properties of the garnet films and practically does not change its optical characteristics. In the proceeding, we have researched the magneto-optical properties of ion implanted (YBiCaSmLu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (FeGeSi) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> garnet films after it was annealed at 270degC. This kind of the experiment is particularly interesting in the matter of annealing process as it reduces the implantation defects and restores crystalline structure of ferrite garnet. We have also determined the spectral dependences of the component of the tensor of dielectric permittivity for the surface of the ferrite-garnet films before and after implantation process. These calculations let us evaluate the influence of implantation on an electronic energy structure of the surface layer for the sample.

Improvements on Faraday Rotation Wavelength and Temperature Characteristics of TbYbBiIG Bulk Crystals in 1550 nm Band

This paper is concerned with the preparation and magneto-optical characterization of the Bi, Tb, and Yb partially substituted rare earth ferrite garnet bulk single crystals of Tb3-x-yYbyBixFe5O12. Here we focus our studies on improvements on the wavelength and temperature dependences of Faraday rotation (FR) by combining two types of bismuth substituted ferrite garnets with opposite FR wavelength coefficient (FWC) and FR temperature coefficient (FTC) signs. The FR and optical absorption spectra were measured and discussed in 1550 nm band. The specific FR of Tb0.91Yb1.38Bi0.71Fe5O12 crystal under magnetic field at saturation was found to be about -1617°/cm at λ=1550 nm, FWC = 0.009%/nm in the wavelength range of 1500–1620 nm and FTC = 3.92×10-5/K at λ= 1550 nm have been obtained due to the compensation effect, which are much smaller than that of YIG.

State of iron atoms in synthetic ferrite garnets and zirconolites—matrices for disposal of actinide-containing waste

Synthetic ferrite garnets and zirconolites containing La, Ce, Gd, and Th as simulators of radioactive actinides have been investigated by 57Fe Mossbauer spectroscopy. The state of iron atoms in the samples studied and their distribution over crystallographically nonequivalent structural positions are established. The crystallochemical formulas are refined and space groups are determined for a number of ferrite garnets and zirconolites.

Magnetoelectric control of domain walls in a ferrite garnet film

A displacement of magnetic domain walls under the effect of an electric field is observed in epitaxial ferrite garnet films (on substrates with the (210) orientation). The displacement of the domain walls changes to the opposite when the electric field changes sign, and it is independent of the direction of magnetization in the domains. The mechanism proposed for explaining the observed phenomenon is based on the inhomogeneous magnetoelectric effect.

Effect of Nd substitution on structure and magnetic properties of NdxDy3−xFe5O12 garnet powders

The properties of light rare earth Nd substitution for heavy rare earth Dy in Dy3Fe5O12 (DyIG) garnet ferrite have been studied. The NdxDy3–xFe5O12 (x = 0, 0.25, 0.5, 0.75 and 1) (Nd:DyIG) garnet powders were prepared by sol–gel autocombustion followed by heat treatment. The structure and the magnetic properties of the annealed powders were measured with X-ray diffraction (XRD), the Fourier Transform Infrared (FT-IR) and the Physical Properties Measurement System (PPMS) techniques. The experimental results indicate that a single Nd:DyIG garnet phase structure can be obtained after the samples annealed above 800 °C. With the Nd substitution content increasing, the average lattice constants of the sample, the a−d super-exchange interaction strengthens and the magnetization of unit cell increase. The maximum saturation magnetization is 13.86 emu/g for x = 1, and coercive force is about 136 Oe, for x = 0.75. The reason of increasing in magnetization with Nd substitution is also discussed.

Magneto-optic imaging: Normal and parallel field components of in-plane magnetized samples

Magneto-optical (MO) imaging has become a powerful tool for determining magnetic properties of materials by detecting the stray magnetic fields. The technique consists in measuring the Faraday rotation, θ F , in the light polarization plane when light travels through a transparent sensitive garnet (ferrite garnet film, FGF) placed in close contact to the sample. For in-plane magnetized samples, the MO image is not trivially related to the sample magnetization, and to contribute to this understanding we have imaged commercial audio tapes in which computer-generated functions were recorded. We present MO images of periodically in-plane magnetized tapes with square, sawtooth, triangular and sinusoidal waveforms, for which we analytically calculate the perpendicular and parallel stray magnetic field components generated by the tape. As a first approach we correlate the measured light intensity with the perpendicular magnetic field component at the FGF, and we show that it can be approximated to the gradient of the sample magnetization. A more detailed calculation, taking into account the effect of both field components in the Faraday rotation, is presented and satisfactorily compared with the obtained MO images. The presence of magnetic domains in the garnet is shown to be related to the change in sign of the parallel component of the stray magnetic field, which can be approximated to the second derivative of the sample magnetization.

A study of the cerium valence in multinary garnet compounds

The valence state of cerium ions in the ferrite garnets {Gd1.96BiCe0.04}Ga1.2Fe3.8O12, {GdBiCe0.5Ca0.5}Ga1.2Fe3.8O12, and {GdBiCe0.25Ca0.25}Ga1.2Fe3.8O12 was studied by L 3 X-ray absorption spectroscopy. Information on the change in the chemical bonding in ferrite garnets upon the violation of lattice completeness was obtained from the shifts of absorption maxima.

Measuring and Visualizing Strong Magnetic Fields by Means of Indicators Based on Garnet Ferrite Films

A method for measuring by means of indicators based on garnet ferrite films the strong magnetic stray fields having intensities of 5–10 kOe that arise in systems of magnets with enormous magnetic anisotropy is described. The method is based on the phase transition from a strip domain structure into a uniformly magnetized state that takes place in garnet ferrite films in magnetic fields with intensities approaching the values of their anisotropy fields. It is shown that, by using indicators with various anisotropy field values, it is possible to obtain a fairly complete pattern of the stray fields localized in a narrow region over the magnets. The resolution limit in the localization region of a strong field is comparable to the width of the strip domains in the indicator and is 1–4 µm. The limiting value of the measured field intensity is equal to the anisotropy field of the indicator material.

Features of the Coercivity of Strained Epitaxial Garnet Ferrite Films

We have studied the influence of the relative film-substrate lattice mismatch in the 0.5–0.85% range on the behavior of coercivity in epitaxial garnet ferrite (EGF) films with compositions (Bi, Sm, Lu, Ca)3(Fe, Sc, Ga, Al)5O12 grown on (111)-oriented gadolinium gallium garnet (GGG) substrates. As the relative film-substrate lattice mismatch increases, the coercivity of EGF films initially grows, passes through a maximum, and then decreases. The maximum in the coercivity is related to periodic localized stresses caused by the formation of a misfit dislocation network whose period is comparable with the width of domain walls. The period of localized stresses is determined by the relative lattice mismatch between the EGF film and the GGG substrate.

Dynamic Systems of Concentric Ring Magnetic Domains in a Highly Anisotropic Garnet Ferrite Film in Magnetic Fields at Infrasonic Frequencies

Dynamic domain structures in a garnet ferrite film with perpendicular anisotropy are investigated in magnetic fields at infrasonic frequencies for the first time. It is revealed that the multidomain film exists in the anger state and that stable dynamic structures with unusual properties are formed in ac magnetic fields at frequencies of 2–3 Hz.

Tetragonalization of (Ca3−x Ax)(Zr2−y Fey)Fe3O12 (A = Ce, Th, Gd) ferrite garnets as revealed by Mössbauer spectroscopy and the Rietveld analysis

Tetragonalization of (Ca3−x Ax)(Zr2−y Fey)Fe3O12 (A = Ce, Th, Gd) ferrite garnets as revealed by Mössbauer spectroscopy and the Rietveld analysis

Microscopic magnetic squeezer

A microscopic magnetic squeezer based on two magnetic domain walls moving along a one-dimensional potential well generated by a stress line in ferrite garnet films is demonstrated. The squeezer can operate on magnetic objects of size 1–200μm and exert compressive forces up to 10pN. The squeezer operation, i.e., the relative motion of the two domain walls, is well controlled by a small external magnetic field modulation. The squeezer has potential applications in microfluidics and also as sensitive pressure gauges for microbiological systems.

Phase transitions in bubble domain structures upon spin reorientation near the compensation point in ferrite-garnet films

The behavior of a hexagonal lattice of bubble domains in a uniaxial thin film of (BiTm)3(FeGa)5O12 ferrite garnet with a compensation temperature of 120 K was studied experimentally in a range of change in anisotropy from the easy magnetization axis to the easy magnetization plane. It is shown that the spin reorientation occurs in the temperature range 185–160 K, in which the angular phase (either \(\Phi _{\left\langle {1\bar 1\bar 1} \right\rangle }\) or \(\Phi _{\left\langle {\bar 111} \right\rangle }\)) and the axial phase Φ:〈111〉 coexist. At 172 K, when the percentages of the angular and axial phases are equal, the lattice parameters of the bubble domains and the domain-wall width change stepwise. At T < 160 K, only a plane magnetic phase exists.

Conduction mechanism in Y 3−2 xCa 2 xFe 5− xV xO 12 garnet ferrites

A series of polycrystalline garnet ferrites with composition Y 3−2 x Ca 2 x Fe 5− x V x O 12 ( x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0), were prepared by the standard ceramic technique to study the effect of Ca 2+ and V 5+ ions substitution on their DC electrical conductivity, thermoelectric power, charge carrier concentration and charge carrier mobility at different temperatures. It was found that the DC electrical conductivity increases linearly with increasing temperature ensuring the semiconducting nature of samples. The lines representing the temperature dependence of σ dc are broken at two-phase transition temperature ( T σ1 , T σ2 = T C) giving three distinct regions (I, II and III). The activation energy for electrical conduction increases going from ferrimagnetic state (regions I and II) to paramagnetic state (region III) through the transition temperature T σ2 (Curie temperature). It also increases going from region I to region II thorough the temperature T σ1 . The dc electrical conductivity does not vary uniformly with Ca 2+ and V 5+ ion substitution. The values of the thermoelectric power were positive for samples of 0.0⩽ x⩽0.6 indicating that the majority of the carrier are holes in these samples while it were negative for samples of x⩾0.8 indicating that the majority of charge carriers are electrons in this samples. Using the values of the DC electrical conductivity and thermoelectric power, the values of the charge carrier concentration and the charge carrier mobility were calculated.

A study of magnetic tunability in a superconductor coplanar resonator using a calcium,vanadium and garnet ferrite

Magnetic tunability of superconducting passive microwave devices can be done bymodifying the characteristics of the medium surrounding the superconductor-based devices,in which the RF signal propagates. The variation of the permeability of a magneticmaterial by a DC magnetic field can achieve this objective. The magnetic material can be aferrimagnetic material, such as a ferrite. An external DC magnetic field is used to modifythe permeability of the ferrite and thus the propagation conditions. A YBCO basedcoplanar resonator having a resonant frequency at 5.6 GHz was used in this study. Aferrite made of calcium, vanadium and garnet (CVG) was chosen because itsproperties are expected to match those of YIG better for this experiment. Severalpositions of CVG ferrite were tried in order to get a good compromise betweenmodulation and degradation of the properties. In the presence of a CVG plate of500 µm thickness, ata distance of 400 µm from the superconductor, a displacement of 18 MHz of the resonant frequency has beenobserved for an applied field of 100 G at 77 K.

Microstructure and hysteresis curves of samarium-holmium-iron garnet synthesized by coprecipitation

An investigation was made into the synthesis and magnetic properties of Sm(3-x)HoxFe5O12 (samarium-holmium-iron) garnet ferrite, as yet absent from the literature. The material in question was synthesized by co-precipitation, starting from hydrated chlorides of rare-earth elements and ferrous sulfate, and the mixed hydroxide co-precipitate was calcined at 1000 °C. Using PVA as a binder, rectangular cross section-shaped compacts were produced by means of steel-die pressing, drying and sintering from 1200 to 1450 °C. The main conclusions of this study were that the coercive force decreases as the sintering temperature increases, and that the effect of substituting holmium for samarium in SmIG is entirely different from that provided by replacing yttrium by gadolinium in YIG, which is the most important result of this work. An in-depth investigation will be necessary to determine the correlation between microstructure/magnetic properties and ceramic processing variables.

Elastic anisotropy and magnetic phase transition of yttrium garnet ferrite

Temperature dependences of elastic moduli describing elastic anisotropy in the rage from room temperature to 600 °C are shown. These temperature dependences are in agreement with available values of elastic moduli and temperature coefficients of the elastic moduli at room temperature. They are in agreement with modern quasi-harmonic theory of crystal lattices . Near 285 °C critical changes of effective elastic moduli due to magnetic phase transition are observed. A correlation was made between experimental and theoretical critical changes of longitudinal and transverse elastic wave velocities for different crystallographic directions. It is proved that the critical change of ultrasound wave velocities of this crystal is connected with the single-ion magnetostriction .

On the local magnetization reversal in front of a domain wall moving in a garnet ferrite film with orthorhombic magnetic anisotropy

The experimentally observed shapes of dynamic domains in garnet ferrite single-crystal films with (110) and (210) orientations are explained in terms of in-plane magnetic anisotropy of these films.