Growth and characteristics of high mobility bubble domain garnets with improved temperature stability

Epitaxial magnetic garnet films containing Ge⁴⁺ and Si⁴⁺ have been grown by conventional dipping techniques using the PbO·B₂O₃ flux system. The minimization of substitution in octahedral sites permits maximum temperature stability for fast data rate bubble domain materials. Stable properties from ?10 to at least 100°C, with bubble diameters of ～6 μm and mobility ～2000 cm/sec/Oe have been obtained.     

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 O₁₂. They show good bubble properties, well suited to practical use.     

Submicron bubble garnets and their characterizations

New Submicron (0.5-1.0 mum diam) bubble garnets have been developed. In order to reduce saturation induction4piMsas low as possible, suitable choice of amounts of nonmagnetic ions substituting for ferric ions in both tetrahedral and octahedral sites were studied in (YSm)3(FeAl)5O12, (YSmLu)3- (FeGaSc)5O12, (YSmLu)3(FeAlSc)5O12and (LaLuSm)3- (FeGa)5O12garnet systems. For example, in (YSmLu)3- (FeAlSc)5O12a film with the following properties was grown; strip widthw = 0.7mum, film thicknessh= 0.7mum, quality factorq=2.8, Curie temperatureTc= 140degC and4piMs=770G. 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.     

The simultaneous multiple dipping of magnetic bubble garnets

The simultaneous growth of LPE films on two-inch diameter Gd3Ga5O12substrates with nominal film compositions in the (YLuSmCa)3(FeGe)5O12system is studied. The effective distribution coefficients of Ca²⁺-Ge⁴⁺, Y³⁺, Lu³⁺and Sm³⁺are discussed and related to the magnetic property variations observed as a function of film growth rate. The approaches for material property control are evaluated and examples given of expected property variation within a stack of epi wafers grown under constant thickness or constant growth rate conditions. A design is shown for a 18 at-a-time and a 30 at-a-time growth holder. Data is presented to indicate the radial thickness uniformity, thickness, saturation magnetization, collapse field and anisotropy field variation typically observed in multiple substrate film growth. A technique for minimizing flux caused mesa formation is evaluated. with comparative data showing the effectiveness of this technique.     

The relationship between uniaxial anisotropy and composition in some magnetic bubble garnets

Data on the relationship between uniaxial anisotropy (Ku) and composition in a series of Ca, Ge substituted rare earth iron garnets for use in magnetic bubble memory devices are presented. These results largely support Eschenfelder's model, and a small modification to this model is proposed which improves the accuracy of the Ku prediction.     

Galvanic overlay fabrication for bubble memory chips on 2-in garnets

Two-inch-diameter wafers containing 56 bubble memory chips of 16 kbit capacity each were fabricated by electroplating. A three-mask level design with a thin-film detector and a minimum feature of 1.5 μm were used. The NiFe films, plated out of a NiFe-sulfamate or a NiFe-citrate bath, had a coercivity of 1.5 Oe, a magnetostriction of 0 to -1 × 10^-6a relative magnetoresistance of 1.8 percent at maximum and a resistivity of 28 μΩcm. A thickness uniformity of ± 2.5 percent was achieved on a Permalloy plating base of 30 nm by balancing the plating conditions. Statistical defects appearing in the transport pattern are significantly reduced by the preplating of a thin Au underlayer into the photoresist windows before the deposition of the Permalloy. The resistance of electroplated Au conductors scattered by ± 8 percent around the mean value and a similar scattering in the dc burn-out current was observed. For reasons of comparison, 16-kbit chips were fabricated using only subtractive techniques. In these experiments Ti-Pd-Au and Ni-Fe layers of the same thickness as the plated ones were evaporated or deposited by sputtering and the microstructures were delineated by ion milling. Comparing the chips fabricated by both technologies, we found no differences in the transport characteristics and the bias-field margins at a drive-field frequency of 100 kHz and for up to 10⁸propagation steps.     

Low temperature delayed recombination decay in scintillating garnets

We study the temperature dependence of delayed recombination decay intensity in a variety of scintillating crystals based on garnet hosts in a wide temperature range 8–500 K. Previous work on several scintillating materials based on silicate hosts showed nonzero constant signal from very low temperatures up to about 120 K. This observation supported a previously suggested hypothesis on low temperature losses of fast scintillation light due to quantum tunneling between the activator and nearby traps. In garnets, the subject of the present article, we observe practically constant signal in the entire monitored temperature range. We thus further test and confirm the quantum tunneling hypothesis in a different class of scintillating materials. We also show that there is no thermal ionization of the activator’s excited state in all materials studied, well above room temperature.     

Some characteristics of ion-implanted bubble chips

The relations between the position of charged walls and the bubble motion around propagation circuits are discussed. Long walls which extend between adjacent propagation loops are revealed by the Bitter technique. The examination of the domain structure in the implanted layer shows the existence of a magnetic gradient which is a function of the distance from the propagation circuits. The switching of magnetization in particular directions of the in-plane field is reported and correlated with the bubble movement. An additional easy axis is observed along the circuits due to shape anisotropy. Propagation margins are very similar to those obtained with permalloy circuits. Fabrication technology as well as design of 16 μm period circuits is discussed. Nucleation and transfer have been achieved with currents in the range of 50 mA to 200 mA. Phase margins of about a quarter of a period are found, and bias field margins fall between 10 and 15 Oe.     

Growth of calcium aluminum germanate garnets in molten bismuth germanate glasses

Selected calcium (and calcium/lead) bismuth germanate melts can partially crystallize, even upon rapid cooling, to small (up to 0.35 mm, but longer in completely crystalline samples) hexagonal needles that appear to be CaBi₂Ge₂O₈. This tendency to crystallize upon cooling can be suppressed by adding small amounts of Al₂O₃. The addition of larger amounts of Al₂O₃ yields a considerable number of well formed garnets that range up to 0.15 mm in size. These crystals can be separated from the adhering glass by appropriate dissolution techniques. The density, refraction, and infrared spectrum of the garnets suggest the formula Ca₃Al₂Ge₃O₁₂. The amorphous garnet-like arrangement of the atoms in these melts appears to be an important factor in their formation.     

小口径浮子流量计温度特性研究

通过计算流体力学(CFD)的方法对15 mm口径的玻璃浮子流量计进行了数值仿真,给出了浮子流量计的速度场、压力场、速度矢量场以及浮子的受力;研究了温度变化对流量造成的影响,并用实验进行了比较.结果表明,数值仿真与实验结果基本吻合.     

Growth behaviors and characteristics of low temperature spin-sprayed ZnO and Al-doped ZnO microstructures

The influence of growth parameters of the spin-spray technique upon the microstructure and electrical and optical properties of ZnO and Al-doped ZnO microstructures was investigated. This investigation was carried out by varying the pH and concentration of the solutions utilized. With increasing pH from 9 to 12, the ZnO films changed from membrane-like microstructures at a pH of 9 to single crystal ZnO rods with hexagonal ends at the pH of 10, and to polycrystal ZnO needle-like tips with random crystalline orientation at the pH of 12. Varying the concentration of the solution brought about a dramatic change in the crystal growth behavior and crystalline orientation, with the least concentration producing rods more uniform and oriented in the c-axis direction. The optical absorption dependence of the ZnO microstructures was also studied by ultraviolet visible spectrophotometer. This investigation will enable optimized low temperature (<100 °C) fabrication of ZnO films by the spin-spray technique with controllable microstructure and properties based on their processing conditions. Furthermore, the influence of Al doping on the electric property, optical property microstructures of the Al-doped ZnO thin films was examined. Increase in Al concentration from 0 to 2 % further reduced the resistivity of the ZnO films by 3 orders of magnitudes from 3.4 × 10⁴ to 14 Ω cm; while the Hall mobility increases from 1 to 140 cm²/V s at the same time. The optical photoluminescence measurement of Al-doped ZnO thin films in ultra violet (UV) was also demonstrated.     

Review of bubble detector response characteristics and results from space

A passive neutron-bubble dosemeter (BD), developed by Bubble Technology Industries, has been used for space applications. Both the bubble detector-personal neutron dosemeter and bubble detector spectrometer have been studied at ground-based facilities in order to characterise their response due to neutrons, heavy ion particles and protons. This technology was first used during the Canadian-Russian collaboration aboard the Russian satellite BION-9, and subsequently on other space missions, including later BION satellites, the space transportation system, Russian MIR space station and International Space Station. This paper provides an overview of the experiments that have been performed for both ground-based and space studies in an effort to characterise the response of these detectors to various particle types in low earth orbit and presents results from the various space investigations.     

LPE growth of iron garnets containing Ge4+ and Si4+ for bubble applications

Magnetic garnet films containing Ca²⁺ plus Ge⁴⁺ and/or Si⁴⁺ are of interest for bubble device applications. Extensive property variations can be obtained in compositions having a lattice constant essentially the same as GGG and suitable films are easily grown using conventional LPE dipping techniques. Films of Y_3?xCa_xFe_5?xGe_xO₁₂, where x = 0.0 to 3.0, have been prepared on GGG substrates and have bubble diameters from sub-micron sizes to over 150 μm. Preferred device materials having moments between ～ 200 and 500 gauss with bubble diameters of ～ 1 to 6 μm have stable bubble properties from well below ?10 to at least 120°C and mobilities of ～ 2000 cm/sec/Oe. The effect of growth conditions and melt composition on bubble properties are discussed.     

Permeability spectrum of garnets

A detailed study of permeability spectra of polycrystalline pure and Aland Gd-Substituted garnets has been carried out for different values of grain diameter and magnetisation. The spectra are of three types—resonance, relaxed and mixed. It has been shown that the resonance spectra occur when the closure demains are absent and the domain wall is anchored at the grain boundary. The relaxed spectrum is found for domains having closure flux while the mixed spectrum is an indication of simulataneous presence of grains with and without closure domains.     

Growth rate of a vapor bubble in an underheated liquid

On the basis of model representations developed earlier the author has obtained an analytical solution of the problem of vapor bubble growth on a wall in an underheated liquid. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 778–780, July–August, 2000.     

A comparison of frequency limited bubble device performance and material characteristics

We have observed the propagation margins as a function of frequency and temperature for a simple half-disk type test circuit fabricated on an (YSmLuCa)3(FeGe)5O12film. We have also measured the temperature dependence of the stripe width, anisotropy field, collapse field, mobility and dynamic coercivity. The frequency dependence of the margin demonstrates that in this circuit, the material is velocity limited above 300 kHz. In the range -20°C to +60°C, the upper and lower margin limits at a given frequency track the collapse field. Over this same temperature range, the mobility varies from 500 to 850 cm/sec-Oe and we conclude that the mobility is not the parameter which limits the device performance. The calculated saturation velocity is independent of temperature in this region and we propose that it is responsible for the failure of the circuit at the highest frequency. In the range from -20°C to +60°C, the coercivity becomes appreciable and the circuit performance deteriorates due to a decrease in the effective drive field.     

Preparation of single crystal films of magnetic bubble materials—rare earth yttrium iron gallium garnets by liquid phase epitaxy and their physical properties

The liquid phase epitaxial growth of rare earth-substituted magnetic garnet films suitable for magnetic bubble domain application by both vertical and horizontal dipping using PbO and B₂O₃ as flux is reported. The dependence of various parameters on lead incorporation in the films present as inhomogeneity has been studied.     

Growth of a bubble of noncondensing gas injected into a liquid

The solution of the problem of growth of a gas-vapor bubble injected into a liquid is obtained. The growth of the bubble depends on mass transfer in the gas phase and heat transfer in the liquid phase. Experimental and theoretical data are compared.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 6, pp. 978–989, June, 1977.     

Thermal expansion of some garnets

Lattice constants of the garnets {Gd₃} [Gd_0.03Ga_1.97] (Ga₃)O₁₂, {Y₃} [Y_0.505Ga_1,495] (Ga₃)O₁₂, Y₃Fe₄GaO₁₂, {Y₃} [In_0.6Ga_1.4] (Ga₃)O₁₂, {Ca₂La} [Zr₂] (Ga₃O₁₂, {Y_1.05Ca_1.95}Ti_1.95Ga_3.05O₁₂, Ca₃Sn₃Ga₂O₁₂, {Ca_2.5Zr_2.5} [Zr₂] (Ga₃)O₁₂, {Na₂Ca} [Zr₂] (Ge₃)O₁₂ have been measured in the temperature range 296–1400°K. The most important results are: 1) Crystals in the system {Y₃} [Y_xGa_2−x] (Ga₃)O₁₂ are potentially good substrates for epitaxial films of the system Y₃Fe_5−xGa_xO₁₂ and 2) Our Czochralski grown crystals of GdGaG actually have the formula {Gd₃} [Gd_0.03Ga_1.97]-(Ga₃)O₁₂; the difference in the thermal expansions of the stoichiometric and Czochralski-grown materials is not significant.     

Heat and mass transfer characteristics of a constrained thin-film ammonia-water bubble absorber

A study of absorption of ammonia vapour bubbles into a constrained thin-film of ammonia-water solution is presented. A large-aspect-ratio microchannel constrains the thickness of the weak solution film and ammonia vapour bubbles are injected from a porous wall. A counter flowing coolant in a minichannel removes the generated heat of absorption. Experiments and a simple one-dimensional numerical model are used to characterize the absorber performance at a nominal system pressure of 6.2 bar absolute. Effect of varying the mass flow rate of the weak solution, vapour flow rate, solution inlet temperature, and coolant inlet temperature on absorption heat and mass transfer rates and exit subcooling are discussed. Two absorber channel geometries, each of 600 μm nominal depth, are considered: 1) a smooth-wall channel, and 2) a stepped-wall channel that has 2-mm deep trenches across the width of a channel wall. Results indicate that the reduction in coolant inlet temperature significantly enhances the mass transfer rates in both absorber geometries. While the stepped-wall geometry exhibits higher mass transfer rates at lower coolant inlet temperatures of 30 °C and 40 °C, the smooth-wall channel shows higher mass transfer rates at the highest coolant inlet temperature of 58 °C. Both absorption limited and residence time limited conditions are observed with variation of weak solution flow rate at fixed vapour flow rates.