Garnet System Research Articles

Kathodo- und Photolumineszenz der Seltenerd-aktivierten Granatsysteme Y3-xGdxM2GaGe2O12 (M = Mg, Zn)

Abstract The optical properties of the self-activated garnet systems Y3-x GdxM2GaGe2O12 (M = Mg, Zn) activated with Ce, Pr, Eu, Tb are strongly influenced by an energy transfer between defect centers of the host and the activator ions. The luminescence properties are studied as a function of the parameter x for M = Mg, Zn.

A new model for handling input

Although there has been important progress in models and packages for theoutputof graphics to computer screens, there has been little change in the way thatinputfrom the mouse, keyboard, and other input devices is handled. New graphics standards are still using a fifteen-year-old model even though it is widely accepted as inadequate, and most modern window managers simply return a stream of low-level, device-dependent input events. This paper presents a new model that handles input devices for highly interactive, direct manipulation, graphical user interfaces, which could be used in future toolkits, window managers, and graphics standards. This model encapsulates interactive behaviors into a few “Interactor” object types. Application programs can then create instances of these Interactor objects which hide the details of the underlying window manager events. In addition, Interactors allow a clean separation between the input handling, the graphics, and the application programs. This model has been extensively used as part of the Garnet system and has proven to be convenient, efficient, and easy to learn.

Optical recording aspects of rf magnetron-sputtered iron-garnet films

The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare-earth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording. This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-Å Co and 9-Å Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y3−xBixFe5O12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor εij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240- and 248-nm wavelengths and a bismuth concentration up x=1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components ε′12 and ε■12 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x=1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co2+- and Co3+- substituted iron garnets and barium hexaferrite BaFe12O19. Finally, the spectral dependence of the magneto-optical figure of merit 2ΘF/α of (Y,Bi)3Fe5O12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal diffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline iron-garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for improving the film texture. Under favorable sputtering conditions single- and polycrystalline bismuth-iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence.

Mössbauer studies of mixed and substituted garnets

We report here our57Fe Mossbauer studies on the mixed and substituted iron garnets. Magnetisation studies on substituted SmIG system {Sm3−x Cax} [Snx Fe2−x](Fe3)012 (0.2≤x≤1.8) show that the Tc decreases as x increases. We attribute this to the reduced strength of a-d interaction as a result of dilution of a-site. While the Mossbauer spectra seem to reflect this, an interesting feature is the unresolved hyperfine spectrum seen at 80K for x=1.0, even though the transition temperature (Tc) is 285K. For this concentration, varying the rare earth ion from Sm to Er, results in very similar spectra. We speculate spin glass behaviour for x=1.0. In mixed and substituted garnet system {Gd2.5R0.2Ca0.3} [Sn0.3Fe1.7](Fe3)012 (R=Y, Sm, Eu, Ho and Er), we observe well resolved spectra with no change in the hyperfine field with substitution of rare earth. This is consistant with the dominance of a-d interaction in these systems.

Theory of Co2+ exchange isolation in ferrimagnetic spinels and garnets

The previously reported mechanism of exchange isolation that was proposed to explain the absence of strong positive magnetocrystalline anisotropy effects from Co2+ ions in LiTi spinel ferrite is approximated by a three-cation superexchange model. This simplified system is then analyzed in terms of the dependence of the single-ion Co2+ anisotropy contribution on magnetic dilution. To account for the reduced anisotropy effects in the presence of strong spin-lattice relaxation, Co2+ is considered to act as a paramagnetic ion through decoupling from the exchange fields of the iron sublattices by magnetic dilution. The exchange-isolation concept is based on selective clustering of Li1+ and Ti4+ dilutant ions that results from the minimization of the total energy comprised of (i) magnetic exchange energy, (ii) lattice electrostatic energy, and (iii) crystal-field stabilization energy. Each of these contributions is discussed in terms specific to the spinel lattice and, in particular, to the ionic distributions surrounding the octahedral site occupied by the Co2+ ion. The model is also tested qualitatively by comparing its predictions with published experimental results for the ferrimagnetic CaV garnet system.

Redistribution of Aluminum Ions During Processing of Sialon Ceramics

Precise determinations of the variation in Al concentration in β‐sialon grains of the garnet and cordierite sialon systems were made by means of quantitative energy‐dispersive X‐ray analysis in an analytical electron microscope. Different signs of the concentration gradients in the grain indicate differences in secondary crystallization mechanisms, while Al distributions with respect to grain size indicate a changing glass‐silicon nitride compatability during crystallization. The technique was also applied to the glassy grain‐boundary phase allowing the determination of the glass‐forming region of the cor‐dierite‐sialon system. A detailed evaluation of errors in analytical transmission electron microscopy (AEM) is described.

The Jahn-Teller effect of Mn3+ions in YIG: magnetocrystalline anisotropy

The temperature dependence of the first anisotropy constant of the garnet system Y3Fe5-xMnxO12 (x=0.006, 0.043) is reported. From the experimental results the single Mn3+ ion contribution k1 to the anisotropy constant is deduced and analysed. It is shown that the observed large and positive values of k1 may be explained on the basis of the existing theory of the Jahn-Teller effect of the octahedrally coordinated Mn3+ ion.

Cation distribution in Eu-Sc-Fe garnets

The cation distribution has been studied with 57Fe Mössbauer spectroscopy in the garnet system Eu 3− y Sc 2+ y Fe 3O 12 with y = 0.0, 0.2 and 0.5. It is shown that the previously proposed cation distribution is not correct. The problem of possible impurities in the investigated system is discussed in detail. Several possible cation distributions are considered compatible with Mössbauer data. Mössbauer results combined with the composition dependence of lattice constants show that the tetrahedral sites are accessible to Sc 3+ ions. The system studied is a second example of a garnet structure in which Sc 3+ ions are found at the tetrahedral sites. A small fraction of Sc 3+ ions for the samples y = 0.2 and 0.5 is also found at the dodecahedral sites.

Inhibitors in LPE growth of garnets

The growth rate of LPE growth garnets can be reduced considerably by the addition of small amounts of group II oxides. This effect can be helpful for the controlled growth of very thin garnet films for sub-micron bubbles and optical devices. The largest effect was found with the addition of Mg 2+ and Ca 2+, resulting in a maximum decrease of the growth rate of approximately 70%. A semi-empirical formula was used to describe the growth rate as a function of the dipping temperature. The change in the growth rate on the addition of the inhibitor ion at constant temperature was found to be proportional to ( aMO)/( aMO+2 Ln 2O 3), where M is a group II element, Ln 2O 2 is the sum of the yttrium and RE oxides in the melt, and a is the inhibitor factor. The value of the inhibitor factor depends on both the inhibitor ion as well as the composition of the garnet. The lowering of the growth rate on the addition of an inhibitor ion is explained by the introduction of an extra growth resistance due to the charge compensation mechanism of the divalent ions. The influence of the different charge compensation possibilities in the garnet system is examined and the relative importance of these possibilities for charge compensation is discussed.

Electric field gradients in EuScFe garnets

The electric quadrupole interactions at the octahedral, tetrahedral, and dodecahedral sites in the Eu 3− y Sc 2+ y Fe 3O 12 (0 ≤ y ≤ 0.5) garnet system were studied with 57Fe and 151Eu Mössbauer spectroscopy. The electric field gradient tensor at the three sites was calculated using a monopole-point-dipole model. It is shown that the dipole contribution to the electric field gradient tensor is not negligible even for very small values of the oxygen dipole polarizability. The importance of the overlap and second-order 4 f contributions is discussed.

Magnetic properties of Eu-Sc-Fe garnets studied with the Mössbauer effect

Magnetic properties of the garnet system Eu3-ySc2+yFe3O12 for 0 ⩽ y ⩽ 0.5 have been studied with 57Fe and 151 Eu Mössbauer spectroscopy. The system is shown to have a ferrimagnetic structure. Both, the ordering temperatures and the hyperfine magnetic fields at the 57Fe nuclei are found to increase with an increase in y. The iron magnetic moments at the octahedral and the tetrahedral sites are non-collinear. The average canting angles at these sites are determined and used for the calculation of the magnetic moments. Good agreement is obtained between the calculated and the experimental moment for the y = 0.0 sample. The determined magnetic properties are consistent with the recently proposed cation distribution in this system.

Spectroscopic properties and 3 μm stimulated emission of Er3+ ions in the (Y1−xErx)3Al5O12 and (Lu1−xEr3)3Al5O12 garnet crystal systems

Detailed spectral physical investigations of the (Y1-xErx)Al5O12 and (Lu1−xEr3)3Al5O12 garnet systems in a wide Er3+ ion concentration range (x = 0.003 to 1) is carried out. The calculation of the ωt intensity parameters in terms of the induced electric dipole transition theory is completed, and the influence of the data on hypersensitive transitions, as well, as the role of the TR3+ ion wavefunction choice to the results of said calculation is discussed. The estimation of the contribu-tion, stipulated by the induced oscillating dipole moments of the ligands in the value of the ω2 parameter is carried out. Intermanifold luminescence branching ratios for all initial laser states of the Er3+ ions connected with the stimulated emission process are calculated. The possibility of using the concept of “spectroscopic quality” of an activated medium in the case when the intensity parameter ω2 ≠ 0 is discussed. The precise measurements of 3 μm stimulated emission spectral composition at ∼ 110 and 300 K are carried out. The energy of the Stark levels of the 4I11/2 and 4I13/2 manifolds is defined. All 3 μm induced transitions are identified and the laser kinetics at their wavelengths is studied. [Russian Text Ignored].

New bubble garnet films with orthorhombic magnetic anisotropy and high mobility: (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG

New orthorhombic magnetic anisotropy garnet liquid phase epitaxial films with high mobility and low coercivity, (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG, have been successfully obtained. There are no hard bubbles, and wall states are either S = 0, 1, or −1. For 2 μm bubble material (YBi)3(FeGa)5O12/(110)GGG, mobility is μw = 85 m/s Oe and saturation velocity is Vs ≃130 m/s. For 6 μm bubble material (YTmBi)3(FeGa)5O12/(110)GGG, μw = 23 m/s Oe and Vs ≃130 m/s are observed. Vs ≃130 m/s for 2 μm bubble material assures bubble transfer at more than 10 MHz in a current access dual conductor device and utilization of the material for a magneto-optic readout head. Orthorhombic anisotropy for these materials is mostly growth induced. Growth-induced perpendicular anisotropies are not observed for eight other garnet systems on the (110)-GGG. Growth-induced orthorhombic anisotropy energy for Bi containing garnets is discussed using Gyorgy’s phenomenological parameters, A and B, compared with growth-induced anisotropy for (111)-oriented garnet films. A unique behavior of Y3+ in Bi containing garnets supports perpendicular anisotropy for orthorhombic anisotropy materials.

LPE of LuLaSmGaFe garnet from a PbO-V2O5 flux

A flux for garnet systems prepared from a PbO and V2O5 mixture has been found advantageous for thin film growth by LPE. There is reduced garnet solubility which leads to slower growth rates. A study of growth kinetics which are interpreted in terms of published models indicates a reduced kinetic constant. Melt equilibrium of the LuLaSmGaFe garnet in the PbO-V2O5 flux system was extensively examined over a wide temperature range. Relationships between film and melt compositions are interpreted in the context of an ideal solution theory for liquid and solid. The relationship between La and Ga interaction in this melt system is examined to reveal effects of growth temperature. Suggested modes for empirical adjustment of the equilibrium model to encompass growth rate effects are briefly discussed.

Growth and characterization of Al-substituted iron garnets for submicron diameter bubble films

Al-substituted rare-earth iron garnet films have been grown that support submicron diameter bubbles. In developing small diameter bubble films, reduction of the saturation induction of a film, 4πMS, is very important because power consumption in drive coils and chip heating increase drastically with higher magnetization. Aluminum ions have been found to be one of the most suitable substitution ions for this purpose. Moreover, owing to the small ionic radius of Al ions, it is easy to meet the lattice matching requirement between films and GGG substrates without lattice adjusting ions such as lutetium. Submicron diameter bubble films are easily grown by the conventional LPE technique in the garnet system (YSmGd) 3 (FeAl) 5 O 12. They show good bubble properties, well suited to practical use.

Magnetic loss and domain-wall mobility in magnetic bubble garnet films

Magnetic loss and domain-wall mobility have been studied in the bubble garnet system (YSmLuCa)3(FeGe)5O12 and in large gyromagnetic ratio (high-g) garnets such as (LaTmCa)3(FeGe)5O12, (YErCa)3(FeGe)5O12, and (YEuCa)3(FeGeSi)5O12. The resonance line width ΔH increases as the concentration of the rare-earth ion in the film increases and decreases as the saturation induction 4πMs increases. The product MsΔH depends only on the rare-earth ion in the film and its concentration. We consider this product as a magnetic loss parameter because it is proportional to the concentration of the rare-earth ion, which is closely related to the magnetic loss energy of the garnet system. The modified Landau-Lifshitz damping parameter Λ(≡λ/γ2; λ: normal Landau-Lifshitz damping parameter; γ: gyromagnetic ratio) is found to be proportional to MsΔH. It is shown that Λ is preferable to the Gilbert damping parameter α and λ itself in studying the dynamic properties such as domain-wall mobility.

Submicron bubble garnets and their characterizations

New Submicron ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5-1.0 \mu</tex> m diam) bubble garnets have been developed. In order to reduce saturation induction <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4\piMs</tex> as low as possible, suitable choice of amounts of nonmagnetic ions substituting for ferric ions in both tetrahedral and octahedral sites were studied in (YSm) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeAl) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , (YSmLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> - (FeGaSc) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> , (YSmLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> (FeAlSc) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> and (LaLuSm) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> - (FeGa) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> garnet systems. For example, in (YSmLu) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> - (FeAlSc) <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> a film with the following properties was grown; strip width <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w = 0.7\mu</tex> m, film thickness <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h= 0.7\mu</tex> m, quality factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q=2.8</tex> , Curie temperature <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Tc= 140\deg</tex> C and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4\piMs=770</tex> G. The temperature properties of those films could be improved drastically by doping with a small amount of Gd ion. Wall mobilities μw of those films are in the region from 200 to 500cm/s/Oe. Preceding these material studies, several film characterization methods have been investigated. Film thickness was measured by Fluorescent X-ray method, strip width by using a highly sensitivity TV camera, and bubble collapse field by FMR resonance technique respectively.

Site preference of iron, gallium and aluminum in quasibinary mixed garnets

The temperature dependence of the equilibrium distribution of Ga resp. Al substitutions over the a-and d-sites in single crystal yttrium iron garnet has been determined from magnetization measurements for substitution levels 0 < z < 1.5 and equilibrium temperatures between 773 and 1773 K. Including literature data derived by different experimental methods for as grown samples of various substituted garnet systems with 0 < z < 5 it is shown that the cation distribution observed on single crystals and polycrystalline samples can be well described by a thermodynamic equilibrium distribution model with two stabilizing energies as fitting parameters. The model includes the influence of the level of substitution and of the actual distribution on the effective site stabilizing energy. By a least error fit to the experimental data the two fitting parameters are determined in terms of the site stabilizing energies for the end member garnets with substitution levels z → 0 and z → 5, respectively: 0.272eV and 0.230eV for Ga substituted yttrium iron garnet: 0.178eV and 0.132eV for Al substituted yttrium iron garnet; 0.26 eV and 0.11 eV for Ga substituted yttrium aluminum garnet; 0.20 eV and 0.15eV for Ga substituted europium iron garnet.

Molecular-field coefficients of Tm3Fe5O12

The molecular-field coefficients of Tm3Fe5O12 were determined by a trial and error procedure used previously in the determination of coefficients for other members of the rare-earth iron garnet family. Since an error was detected in the application of the original computer program, a corrected set of coefficients is also given for these compositions. Results of calculations of magnetization-temperature curves of ferrimagnetic garnet systems with mixtures of rare-earth ions are also reported.

Comparison of eight mixed garnet systems for 7 μm-period bubble devices

An extensive investigation of eight mixed garnet systems, totally 22 compositions with the same l values (0.2μm), was carried out for realization of high bit density bubble memory chips employing 1.8μm diameter bubbles in 7μm-period devices. The eight systems are YSmLuCaGe, YSmTmCaGe, YEuLuCaGe, YEuTmCaGe, YSmLuGa, YSmTmGa, YEuLuGa and YEuTmGa garnets grown on (111) GGG substrates. In order to fill in the material gap between Sm- and Eu-based garnets, YSmEuLuCaGe and YSmEuTmCaGe garnets were also studied. Comparison was made with respect to static (4πMs, Ku, HK, TC, A) and dynamic (μw, ϑ) properties, as well as Hco1 temperature dependence. Q-factor was varied by changing rare earth content ratio, but l and film lattice parameters were left essentially unchanged. From the dynamic and temperature properties viewpoints, it was revealed that YSmLuCaGe, YSmTmCaGe, EuLuCaGe, YSmEuLuCaGe, and YEuTmGa garnet systems are candidate materials, with l=0.2μm and Q?4, for practical applications which utilize 7μm-period patterns.