D.H. Smith

Resonant Motion of Domain Walls in Yttrium Gadolinium Iron Garnets

The radio frequency (rf) susceptibility of a series of yttrium gadolinium iron garnets was investigated in the frequency range 40–160 MHz. Resonant behavior was observed for most compositions, and the effective mass of the domain walls and the Landau‐Lifshitz damping parameter were determined. The damping parameter was found to be approximately the same for the yttrium and gadolunium ions with the value λ ≃ 1.6×107 rad sec−1.

Material requirements for circular magnetic domain devices

The material requirements of circular cylindrical domain devices are discussed. The current status of the search for circular domain materials is summarized with respect to the anisotropy field H k and the saturation magnetization M s by a chart showing the influence of these quantities on the size, stability and mobility of the circular domains. A preferred region is defined on the chart and representative materials are plotted. At the present time, the preferred region is most closely approached by certain mixed rare-earth orthoferrites and the aluminum substituted hexagonal ferrites.

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

Abstract Epitaxial magnetic garnet films containing Ge 4+ and Si 4+ have been grown by conventional dipping techniques using the PbO·B 2 O 3 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 μ m and mobility ∼2000 cm/sec/Oe have been obtained.

Three garnet compositions for bubble domain memories

The choice of magnetic garnet compositions for bubble memories is always a compromise dictated by the material requirements generated by the specifications on the memories. The three compositions reported, Y2.62Smo.38Fe3.85Ga1.15O12, Gd2.lLuO.9Fe4.4Al0.6O12, and Yl.92Sm0.1Ca0.98Fe4.02Ge0.98O12, represent three examples of such a compromise. The first composition is excellent for use in circuits operating at 100 KHz over a temperature range of -20° to 80°C. The second has a mobility up to 5000 cm/sec/0e and is capable of very high speed operation at the sacrifice of stability toward temperature. The third exhibits excellent stability toward temperature and has operated at 1 MHz but is compositionally more complex.Melt compositions for film growth and a summary of magnetic properties are presented for the three compositions. Factors to be weighed in composition selection for bubble domain memories are discussed.

The temperature dependence of the anisotropy field and coercivity in epitaxial films of mixed rare‐earth iron garnets

The temperature dependence of the anisotropy field Hk and the domain‐wall coercivity Hc have been measured for three different epitaxial films of mixed rare‐earth iron garnets with the nominal compositions Er2Eu1Ga0.7Fe4.3O12, Y1Eu1.85Yb0.15Al1.1Fe3.9O12, and Eu1.7Er1.3Al0.7Ga0.8Fe3.5O12. Each of these garnets supports bubble domains. The anisotropy field was measured using an optical magnetometer, and analytical expressions are developed which relate the optical magnetometer parameters to the anisotropy field. These measurements show that the anisotropy field decreases with increasing temperature at about −1%/°C at 20°C for all three samples. The coercivity, again measured by an optical technique, was also found to decrease with increasing temperature. The coefficient ranged from −1.3%/°C to −3.0%/°C at 20°C depending on the sample. The largest total change in Hc for one of the samples was a factor of 310 over the temperature range −106°C to +80°C. The temperature variation of the saturation magnetizatio...

Characteristics of Temperature‐Stable Eu‐Based Garnet Films for Magnetic Bubble Applications

Epitaxial garnet films Y3−xEuxAlyFe5−y O12, with x=1.5–2.0 and y=0.7–1.2 and small additions of Yb, are reported: with 1–7‐μ bubbles; with bubble diameters that are relatively constant versus temperature; and in which bubble velocities greater than 1500 cm/sec have been observed. These materials show promise for bubble device applications.

Damping of domain wall motion in rare‐earth iron garnets

Landau‐Lifshitz damping parameters deduced from domain wall mobility measurements are reported for a number of rare‐earth iron garnets. These damping parameters are compared with the ones obtained from ferrimagnetic resonance experiments.

Magnetic properties of flux grown uniaxial garnets

Static and dynamic properties of bubble domains are given for a number of mixed rare earth and related iron garnets that have growth induced noncubic magnetic properties that are of interest and, in some cases, are useful for bubble-domain device applications. Rules for predicting domain alignments related to {211} facets, the various cuts for obtaining useful platelets, and compositional controls for obtaining temperature independent properties are also outlined.

Controlled adjustment of bubble domain parameters in epitaxial garnet films by thermal annealing

Controlled adjustment of the bubble domain collapse field has been demonstrated in epitaxial garnet films of nominal composition Y2.6Sm0.4Ga1.2Fe3.8O12 using a thermal annealing technique to redistribute gallium ions between the tetrahedral and octahedral sites in the garnet lattice. This technique involves annealing each film at two different temperatures, the first of which establishes equilibrium at a known temperature. Analysis, based on bubble domain theory, shows that the measured parameters after thermal equilibration can be used to calculate the change in saturation magnetization which will lead to the desired values of the bubble domain collapse field. The change in magnetization can be related to the required change in the equilibrium annealing temperature, Ta, from the derivative d(4πMs)/dTa. The value of d(4πMs)/dTa has been found to be approximately constant for 900≲Ta≲1200 °C and is equal to 0.35≲G/°C. By using this technique, the bubble domain collapse field can be changed by more than 10 O...

Hexagonal ferrites for bubble domain devices

Abstract Large crystals of aluminum substituted magneto-plumbite have been grown from a PbO·PbF 2 ·B 2 O 3 flux. Such materials may be used in bubble domain logic and memory devices. Quality is good for crystals grown with the c-axis horizontal at the bottom of the container while employing a negative vertical temperature gradient.