John B. Ings

Hydrothermal growth of potassium titanyl arsenate (KTA) in large autoclaves

Solubility and phase relations were investigated for selected K/As ratios in KH 2 AsO 4 -KOH solutions at 600°C and 2040 atm. All initial data were obtained with 5 mm diameter x 50 mm long platinum capsules in Tem-Pres type autoclaves. The most favorable results were repeated in Morey type autoclaves of 2.2 cm diameter. The P-V-T data were generated and extrapolated for use in gold liners and Rene 41 autoclaves with a pressure balancing method. Transfer to the 3.8 cm diameter x 46 cm long autoclaves with gold liners was achieved. Both nutrient and larger seed crystals were grown from a K 2 WO 4 -Li 2 WO 4 flux. The internal and external degrees of fill were adjusted to obtain a balance of pressure at 1700 atm and 590°C. Initial growth runs were made for 1–2 weeks under a gradient of 30°C with a 4 molar KH 2 AsO 4 mineralizer. Natural facet seeds were employed first while later runs utilized (011) cut and polished seeds.

Growth Of Bismuth Garnet Films For High Figure Of Merit Faraday Effect Devices

Single crystal films of the bismuth substituted iron garnets have been grown by liquid phase epitaxial (LPE) procedures onto GGG or CMZGGG substrates. For switchable devices, both the optical figure of merit, defined by θ/α (0 = Faraday rotation and a= optical loss) and the magnetic properties must be controlled. We have prepared films of the type BixRE3-xFe5-yGay012 on GGG (ao = 12.383A) substrates with figures of merit greater than 1°/pm or 2°/dB at 550 nm. Single rare earths (RE) or combinations of Tm, Yb, Lu, or Y are used with 0.4 <x <0.6 and 0.8 <11. <1.2. The anisotropy field Ht, magnetization 4TrMs, and collapse field must be low to obtain switching. The optical figure of merit can be doubled by employing substrates of CMZGGG (a0 = 12.495A) to incorporate more Bi. Films of the type BixTmyGdzY3-x-y-zFe5-tGat012 were prepared by LPE growth. These films approach 4°/db at 550 nm, had also a high Curie point of 170°C, and fulfilled all magnetic parameters for switching. Switchable films are useful for structured devices such as displays, printers, modulators, pattern recognition, or cross bar switches. Many of these have been prepared with 64 to 128K independent elements. If the highest figure of merits are desired and mag-netic parameters are not critical, the amount of Bi can be increased further by using NdGG (ao = 12.51A) (or other high ao substrates such as GdScGG (a0 = 12.55A). These films are prepared in 1 - 10μm thicknesses but can be grown up to 50 - 400pm by single or multiple film methods. Thus high absolute rotations of 45 - 90° can be obtained. Such films may be used in optical isolators for fiber optics at 1.30 - 1.50μm where low insertion loss is required. The consistent growth of both low resonant linewidth (AH) and high Bi films for optical guided wave and magnetostatic wave interactions is still a challenge.

Seeded solution growth of β″-Al2O3 single crystals

Abstract Single crystals of β ″- Al 2 O 3 were grown by the top seeded solution method from a Li 2 O - V 2 O 5 flux. Similar methods were also applicable to liquid phase epitaxial growth of β ″- Al 2 O 3 films on selected substrates. Seed crystals and substrates included β ″- Al 2 O 3 , β - Al 2 O 3 , MgAl 2 O 4 and LaMgAl 11 O 19 . Phase diagram studies provided an optimum range of compositions and temperatures for growth in platinum containers. A composition of 23 wt % Na 2 O ,54 wt % Al 2 O 3 , and 23 wt % LiVO 3 enabled growth to occur at temperatures of 1450–1550°C. Single crystal platelets of cm size were grown with fair quality but still contained small flux inclusions which led to delamination. Epitaxial films of up to 100 μm thickness were successfully grown on [111] oriented MgAl 2 O 4 .

Chemical modification of magneto‐optic garnet film properties

Single‐crystal magneto‐optic garnet films of composition (BiTm)3(FeGa)5O12 have applications to spatial light modulators, optical isolators, and magnetic‐field sensors. These as‐grown films have a coercivity under 1 Oe and can support cm‐size stable domains. It has been found that chemical treatments with oxidizing or reducing gases can reversibly modify the magnetic properties. Treatments are performed at 400–700 °C for fixed times. Reducing treatments dilate the x‐ray lattice constant up to 0.1%, introduce Fe2+ monitored by increased optical absorption at 1.00–1.06 μm and decrease Faraday rotation about 5% over the visible spectrum. Oxidation can partially or totally reverse these parameters. Magnetic measurements on the bulk film show that coercivity can be finely controlled, square hysteresis loops attained, and domain‐wall mobility changed. At the same time the initial perpendicular anisotropy Hk of 8–12 kOe is decreased while the saturation magnetization (4πMs) of 100–150 G is affected to a minor de...

Excimer laser processing of magneto-optic garnet films

A 248‐nm KrF excimer laser was used to introduce defects into single‐crystal GGG substrates and magneto‐optic bismuth garnet films. The number, size, and distribution of defects can be controlled accurately in the 1–100‐μm range. Defect introduction raises the coercivity of the films, controls their switching behavior, and modifies the hysteresis loop. Present theories do not explain the coercivity data as a function of defect density.

The temperature dependence of the anomalous effective g value of BiTm:YIG

Bi‐ and Tm‐substituted YIG have shown [V. R. K. Murthy et al., in Digest of INTERMAG Conference (IEEE, New York, 1983)] anomalously low effective g values. The experimentally measured temperature dependence of BiTm:YIG shows that the effective g value decreases with decreasing temperature whereas the simple spin‐wave theory predicts the opposite behavior. A recent paper [A. Lehmann‐Szweykowska et al., J. Magn. Magn. Mater. 54, 1183 (1986)] predicts that the single ion anisotropy and spin‐wave damping also make important contributions to the effective g value. These effects are due to the large crystal field effects of Tm in the garnet crystal host. The ground state of the Tm is J=6, L=5, and S=1. The large orbital angular momentum states enhance the spin‐orbit coupling which is related to the crystal field effect. The temperature dependence of the effective g value was measured by FMR (ferromagnetic resonance) on BiTm:YIG. The experimental temperature dependence is fitted to the theoretical model and exce...