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Experimental 8-μm period magnetic bubble devices have been made using 270/Ne/2E14 + 130/H 2 /2E16 patterned implants on YSm-LuCaGe-IG films previously implanted uniformly with 80/Ne/1E14. For subsequent alignments, the patterned implant was converted, in selected areas, into a relief pattern by phosphoric acid etching. A 2000 A.U. SiO 2 prespacer was deposited next, followed by the deposition and ion beam delineation of 500 A.U. of Permalloy for detection. A subsequent 2000 A.U. spacer was then deposited and patterned with via holes for electrical connection between the Permalloy and a 5000 A.U. Al-Cu layer which was deposited and patterned with plasma etching or ion beam milling. Final passivation and opening of contact windows were standard. All designs at 8-μm period were implemented with 2-μm or larger features. Novel ion-implanted propagation patterns are shown which accomplish merge, inside turns, and double period propagation. A conventional hairpin shape was chosen for the generator, and the structure was placed in a cusp on the strong side of the major loop. Phase and current margins are presented. The minimum generator current varied with the starting anisotropy of the bubble film. The minimum current was about 100 mA in films with H k around 1700 Oe, when the shallow implant was unpatterned. When the shallow implant was patterned, lower values were obtained. An N-shaped transfer gate was studied. The design provides both a strong gradient, to separate the bubble from the implant boundary, and a locally lowered bias region to trap the bubble until the correct in-plane field orientation results in normal propagation. Phase and current margins are shown for transfer-out. A hairpin linking cusps on the two sides of a horizontal loop was found to transfer both ways with good current margins. This gate can be used as an active merge or to reverse the order in a block to overcome topological difficulties in a G-type major-minor loop chip. Using the same idea, a transfer gate was designed which transferred through a write line to the bottom of the minor loops. Good phase and current margins were obtained. A combination of a 2-μm wide implanted channel, a hairpin canductor, and a symmetrically placed Permalloy serpentine has been studied in a nondestructive read-out (NDRO) mode. It appears that the serpentine has too few turns for good averaging of Permalloy domain effects, as these detectors are noisy. An alternate design used a simple Permalloy bar entirely over implanted material. The straight detector produced better signal-to-noise appearance, although at a lower signal level and higher stretch current. Two straight bars were used in conjunction with the channel design. Both detector and “dummy” sense the stripped-out bubble in this case. Low noise and the best figure of merit δV/V ∼ 0.38 percent were obtained In the destructive read-out (DRO) mode of operation. Good signals were also obtained from a straight Permalloy bar located over an unimplanted region, in the DRO mode, with a separated dummy. A valid chip organization for the DRO mode is offered. Thus, all necessary functions have been demonstrated for the design of 8-μm period maior-minor loop-organized bubble devices based on ion-implanted propagation. At least 20-Oe margins are shown for all functions at 40-Oe drive field.

The general magnetic and physical requirements that a material must meet in order to be useful in magnetic bubble devices are reviewed. An approximate expression relating stripe width and film thickness to the material length parameter (l) is presented. The well‐known equations relating anisotropy, moment, Q factor and exchange constant are rearranged, and, combined with the approximate expression for l, result in a convenient set of equations which are useful for materials design and for evaluating magnetic property measurements. The exchange constant (A) of epitaxial bubble garnet films is presented as a function of Curie temperature. Nominal compositions are given in the (YLuSmCa)3(FeGe)5O12 system which will support bubble diameters from 3.0–1.7μm. The range of λ111 values which are needed to implement Ion Implanted Propagation Patterns (I2P2) is presented. An approach is presented for increasing the uniaxial anisotropy in the 〈111〉 crystallographic direction without significantly changing the damping...

Two interesting effects have been experimentally demonstrated for the first time: (1) simultaneous reciprocal and nonreciprocal mode conversion to achieve an isolation effect and (2) magneto‐optic switching between guided and radiation modes. These effects were observed in connection with the construction of a previously proposed thin‐film optical isolator. The isolator consists of a piece of LiNbO3 placed on top of a thin film of yttrium ion garnet (YIG) with a selenium layer to avoid optical contact problems. The isolator, which is 1 cm long, exhibited 10 dB of isolation at λ = 1.15 μm. The observed isolation was better than theoretical predictions and a mysterious isolation direction dependence on mode order was observed. Although the device had 10 dB of insertion loss and required a magnetic field of 40 Oe, with a slight change in wavelength and film composition, it should be possible to reduce the insertion loss and field required to under 1 dB and 0.1 Oe, respectively. These characteristics combined...

In magnetic fields above saturation the specific magneto-optical rotation Φ of yttrium iron garnet decreases linearly up to about 1700 kOe. Several recent high field measurements of the slope of this linear segment S = ΔΦ ΔH have given a wide range of results, suggesting an impurity effect. In low field (

Experimental and theoretical results from our work on current-access technology show promise for high-density, ∼107 bits/cm2, and high-frequency, f 3 (FeGe) 5 O 12 , (LaLuSmCa) 3 (FeGe) 5 O 12 , and (LaLuSm) 3 (FeGa) 5 O 12 , the last appears best suited; some room temperature characteristics of the composition La 0.6 LU 2.1 Sm 0.3 Ga 0.9 Fe 4.1 O 12 are 4μMM, = 470G, μ = 750 cmS−1. Oe−1, d = 1.6 μm, and ΔH c = 2 Oe across a bubble for the threshold of motion. Necessary improvements in processing were made with a radio-frequency, chlorine-containing plasma etch which produced metal patterns identical to those of the etch mask. We anticipate that current-access devices, when compared to conventional field-access devices, will achieve higher data rates, lower power consumption per bit, and greater storage densities with existing processing technologies.

The magnetoresistance of bulk and epitaxial films of YIG(Si) has been previously reported by us (Ref. 10). These results can be summarized by the cubic expression ΔR/R=kl(α2iβ2i–αiαjβiβj) where kl at 300°K is between −0.002 and −0.02 and essentially independent of the value of the applied field once the sample is saturated. Similar results have now been obtained for Eu3Fe5O12 (Si) and Eu2.9Lu0.1Fe5O12(Si). The behavior of Tb3Fe5O12(Si) is dominated by additional phenomena. The relatively large field independent term observed in YIG(Si) is small here. However there is a large, isotropic field dependent term and ‖ΔR‖ increases linearly with H. The value of (1/R) (dR/dH) is positive at 300°K and increases with decreasing T. At the compensation temperature this quantity abruptly changes sign and then decreases rapidly with decreasing T. The absolute value of (1/R)(dR/dH) is continuous except for a break right at the compensation temperature. (It is interesting to note that the addition of Si in the sample dis...

The growth and properties of films of a novel composition, (SmLuCa)3 (FeVSi)5O12, for 4‐μm period Ion‐Implanted Propagation Pattern devices, are described. The use of vanadium substitution to lower 4πMs yields films with high Curie temperatures (Tc =512–524 °K). Small amounts of silicon are added for lattice matching of the films to the substrate and also to increase the Q value. The presence of vanadium in films was also found to substantially increase the Faraday rotation. The bubble size in these films is nearly constant in the temperature range of −50° to +150 °C. The films also have a high mobility and low dynamic coercivity. Preliminary results of bubble propagation in these films in the temperature range −50° to +160 °C are described. It is expected that because of a combination of the desirable magnetic properties, these films will find a widespread use in bubble devices requiring operations to higher temperatures.

The existence of an oxidation mechanism is reported in Ca-doped YIG films, when high temperature annealing is carried out in N2 atmosphere. The annealing were performed at successively increasing temperatures, and optical absorption, lattice parameter and thermoelectric power were measured at each step. Optical absorption was observed going down to a minimum (T = 450°C in one cycle of annealing, T = 400°C in a different cycle) and then rise again. The minimum in absorption corresponds to a maximum of the lattice parameter, while the thermoelectric power is always p-type. Analysis of the data leads to the conclusion that we are observing a reoxidation process, triggered both by temperature and oxygen vacancy concentration. This process is subject to exhaustion. Previous annealing experiments are analyzed in the light of these results.

We have measured the circuit propagation characteristics of magnetic bubble domains in 15 different epitaxial films of Y1.9Sm0.1Ca1Ge1Fe4O12, using a TX propagation circuit with 28.8−μm period. For film thicknesses of 2 μm or less, reliable propagation was observed up to 1.7 MHz. Thicker films ceased to propagate reliably at frequencies as low as 0.5 MHz. Propagation failure is attributed to dynamic conversion of the bubble domain walls, and reasonably good quantitative agreement is shown between our measured critical frequencies and the critical frequencies calculated from a recently published model for dynamic conversion.

Measurements of anisotropy in implanted bubble films indicate that in addition to straining the lattice, implantation also has the effect of suppressing the growth‐induced anisotropy. After annealing at 1000 °C, most of the as‐grown anisotropy is restored, which points to oxygen defects as the most likely mechanism for the effect. The Curie temperature has been found to be lowered by as much as 70 °C by implantation at a typical device dose, and the anisotropy of the implanted layer varies quite rapidly with temperature at elevated temperatures. The results indicate that with proper choice of material parameters and implantation conditions safisfactory bubble propagation can be obtained in high density small bubble diameter devices based on ion‐implanted propagation patterns over a wide temperature range.

Large growth‐induced anisotropies (Ku) arising from the preferential occupation of Ir4+ on octahedral sites have been measured. For YIG with approximately 0.2 Ir atoms per garnet formula unit and Mg2+ as a charge compensator, values of Ku=+4.5×105 ergs/cm3 have been obtained. The induced anisotropy is proportional to the Ir4+ present as deduced from the optical absorption.

The nature and site occupancy of Fe4+centers in Ca-doped YIG films is investigated by studying the symmetry properties of the near-infrared absorption. We apply the recently proposed AVIA (angular variation of induced anisotropy) method: we measure, as the single- -crystal film is rotated relative to a magnetic field, the angular variation of the magnetic linear dichroism, which is the anisotropy property utilized in this case. The AVIA pattern thus obtained is compared with the theoretical angular variations appropriate to the symmetry of the garnet sites. The result we find is a uniform distribution of Fe4+over the a (octahedral) and d (tetrahedral) sublattices. This uniform distribution does not change, in spite of varying Fe4+concentration, after successive annealing treatments in oxidizing or reducing atmospheres. The structural changes through the annealing steps are monitored by X-ray diffraction and the lattice is found to expand, under reducing treatments, only as long as there are Fe4+centers. After all Fe4+ions have been reduced (namely at zero near-infrared absorption), rapid diffusion of oxygen anions is hindered, in spite of the large concentration of oxygen vacancies. All observed effects are explained by a single mechanism: electron deficiency (or holes), in Ca-doped YIG, results in a widespread distribution of Fe 4+ and, effectively, in the presence of O- oxygens.

We have investigated the dynamics of magnetic domain walls in three epitaxial garnet films with g values of 1.07, 4.8, and ≳30, and having wall mobilities of 880, 930, and 820 cm/sec Oe, respectively. Bubble collapse measurements in the films with g=1.07 and 4.8 showed velocity saturation with the approximate values 1500 and 8000 cm/sec, respectively. The film with g≳30 showed no saturation, and velocities up to 6×104 cm/sec were observed. These results are consistent with the expected increase in the Slonczewski and Walker critical velocities with increasing g value. Large g values make it possible to operate magnetic bubble circuits at higher frequencies than is otherwise the case.

The effect of annealing in reducing atmosphere on Ca‐doped YIG films are studied by means of magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) in the near infrared. The LPE films had ‖110‖ and [100] orientation and the Ca content was about 0.1 atoms/formula unit. The MDC spectra are found to change shape dramatically after the first milder reducing treatments, then a definite and constant shape is acquired, the corresponding amplitude scaling down linearly with absorption until attainment of full infrared transparency. Such a behavior suggests the presence in the films of more than one type of Fe4+ centers which are reduced at different rates during the initial treatments, until a single type eventually prevails. Furthermore, an AVIA experiment indicates that the Fe4+ centers being reduced at a faster rate have markedly different orientational properties than the later ones, with in‐plane MLD about 20 times smaller. The results are explained in terms of different acceptor centers being involved in the earlier and later stages of the reducing treatments and are assumed responsible for the recently reported nonlinear behavior and for increasing oxygen‐vacancies concentration of the uniaxial anisotropy constant of YIG:Ca films.

Measurements of oxygen diffusion in YIG : Ca at different oxygen partial pressures have shown that the diffusion rate strongly depends on oxygen vacancy concentration. At very high vacancy concentration this diffusion is quite rapid. For example, with approximately 0.1 vacancies per formula unit the oxygen diffused 0.9 mm in 24 h at 325 °C. It has also been shown that under many conditions the rate limiting process occurs at the surface of the YIG : Ca. An additional thin epitaxial layer having a much higher defect concentration greatly reduces the limitations imposed by the surface.

Garnet films of compositions (EuLaCa)3 (FeGeAl)5O12 which support magnetic bubbles have been grown by liquid phase epitaxy on (110), (111), and (100) substrates of Nd3Ga5O12. In each material, La plus Eu provides the growth‐induced uniaxial anisotropy in (100) films, Ca plus Eu in (111) films, and the combination provides a normal easy axis as well as in‐plane anisotropy in (110) films. General conditions for achieving stable bubbles and large in‐plane anisotropy in (110) films are discussed in terms of the phenomenological theory of growth‐induced plus stress‐induced anisotropy.

A new approach to overcoming the problem of dynamic conversion in high−mobility bubble garnets is described based on large gyromagnetic ratios (high g factors). In a film of Eu1.45Y0.45Ca1.1Fe3.9Si0.6Ge0.5O1 2, a g factor greater than 30 has been obtained, which increases the usable domain wall velocity before onset of dynamic conversion by more than an order of magnitude over comparable bubble garnet films with g approximately 2. Using a circuit period of 28.8 μm, propagation data showing no deterioration in bias margins out to 107 steps were obtained on this film at 1 and 2 MHz.

Ion implanted propagation patterns for magnetic bubble devices provide an approach to higher density through relaxed photolithography. At the same time, the drive field requirements may be reduced, with respect to Permalloy based field access devices. Propagation is studied in the present work at 8 μm period in YSmLuCaGe films. Profiling by relative etch rate and by wafer curvature has led to 80/Ne/1‐2E14+270/Ne/2E14+130/H2/2E16 implantation conditions. Bias field margins vs drive field for 27‐step loops with neighbors on 2 λ centers and in orthogonal orientations on the wafer are presented to demonstrate the feasibility of major‐minor loop organized chips. Crystal symmetry effects do cause the margins for differently oriented loops to be different in the present material, however. The overlap bias range is about 20 Oe extending downward from free bubble collapse. The minimum drive at 40°C appears to be about 35 Oe. Bias margins at 40 Oe drive taken over the temperature range 0–80°C show no anomalies for ...

Measurements of magnetic bubble coercivity in Ga substituted and in Ca‐Ge substituted garnet films capable of supporting 1.7 μm diameter bubbles show that the Ga substituted films have lower coercivity which increases less rapidly with decreasing thickness than in Ca‐Ge substituted films. High temperature annealing experiments indicate that the coercivity may be proportional to the material length and the saturation moment.

Ion implantation of bubble garnets can lower the Curie temperature by 70 C or more, thus limiting high temperature operation of devices with ion-implanted propagation patterns. Therefore, double-layer materials were made with a conventional 2-micron bubble storage layer capped by an ion-implantable drive layer of high Curie temperature, high magnetostriction material. Contiguous disk test patterns were implanted with varying doses of a typical triple implant. Quality of propagation was judged by quasistatic tests on 8-micron period major and minor loops. Variations of magnetization, uniaxial anisotropy, implant dose, and magnetostriction were investigated to ensure optimum flux matching, good charged wall coupling, and wide operating margins. The most successful drive layer compositions were in the systems (SmDyLuCa)3(FeSi)5O12 and (BiGdTmCa)3(FeSi)5O12 and had Curie temperatures 25-44 C higher than the storage layers.

The exchange stiffness coefficients A of tetrahedrally substituted YIG:CaGe and octahedrally substituted YIG:LuSc have been determined over the temperature range of 30 to 300 K. The magnetization M of each sample was measured range of 30 to 300 K. The magnetization M of each sample was measured with a vibrating sample magnetometer. The spin wave dispersion coefficient 2A/M was measured using microwave resonance techniques. Values of A were determined as a function of substitution level, the microscopic site of the substitution, and temperature. The results of this study indicate that the Kirkpatrick and Harris percolation model provides a close agreement with the experimental data obtained in this work. The most significant result of this work is represented by a plot of the room temperature values A versus the Curie temperature of each sample. Data for both systems studied here fall on the same curve. It appears that this general curve will yield values of A for a wide range of substituted garnets. Avail...

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.

The growth‐induced anisotropy, Ku measured on (111) LPE films of Eu3−xCaxSix Fe5−xO12 grown on Sm3Ga5O12 substrates is large and positive (Ku = 4.0 to 8.1×104 ergs/cm3 for x = 0.5). Many experiments have shown that Ku in Eu3−xYxFe5−yGayO12 films is also positive. In films of compositions (YSmCa)3 (GeFe)5O12, the effects of Ca and of Y on the growth‐induced anisotropy are the same in sign and similar in magnitude. Since Ca2+ is larger in ionic radius than Eu3+ or Sm3+, whereas Y3+ is smaller, the simple site selectivity model of growth‐induced anisotropy would predict opposite signs of Ku for the Ca and Y additions. This contradiction shows that ionic radius is not the only relevant parameter which determines growth‐induced anisotropy in garnets, although size differences have been shown to account for the observed effects within the rare earth series. The charge difference between the Ca2+ ions and the rare earth ions, or the pairing of Ca2+ and Ge4+ or Si4+ ions during crystal growth may influence the si...

An approach to overcoming the problem of dynamic conversion in high‐mobility bubble garnets is described based on large gyromagnetic ratios (high‐g factors). In a film of Eu1.45Y0.45Ca1.1Fe3.9Si0.6Ge0.5 O12, a g factor greater than 30 has been obtained, which increases the usable domain wall velocity before onset of dynamic conversion by more than an order of magnitude over comparable bubble garnet films with g approximately 2. The temperature dependence of the important bubble parameters has been measured and a simple bias magnet constructed which matches the steeper than usual variation of the bubble collapse field with temperature. Two different methods of hard bubble suppression are described, one involving short oxygen anneals at ∠1050°C, and the other ion implantation.

The magnetoresistance of bulk and epitaxial films of doped n‐type yttrium iron garnet is reported for the first time. In (111) films a ΔR/R of −0.55% is observed as a saturating applied field H is rotated out of the (111) plane to the film normal. There is no observable change in ΔR/R as H is rotated in the (111) plane, with the current I in various directions in the (111) plane. This isotropy of ΔR/R in the (111) plane has not been observed in other ferromagnetic materials such as iron and nickel and is not understood as yet. The same isotropy in the (111) plane is also observed in bulk yttrium iron garnet. A possible use of this magnetoresistance for magnetoresistive detectors in magnetic bubble devices is discussed.

Unexpectedly rapid oxygen diffusion has been observed at 25–250 °C in YIG films with uncompensated Ca additions of 0.1 to 0.23 atoms per formula unit. A 3‐μm‐thick film originally dark and conducting due to Fe4+ lightened and became insulating in 15 min at 100 °C in a reducing saturated solution of FeCl2. A diffusion distance of ∼0.5 mm has been observed along a film in 25 h at 250 °C. A model is proposed based on the dependence of the diffusion coefficient D on oxygen vacancy concentration. A magnetic bubble garnet film containing Ca, which also lightened at 250 °C, showed no observable changes in the pertinent bubble parameters.