The influence of neutron and gamma irradiation in bubble garnet films

The behaviour of garnet films, containing 3 micronsbubbles, exposed to neutron irradiation and gamma rays is reported. The implanted and non implanted (YSmLuCa)3(FeGe)5O12epitaxial garnet films were irradiated with fast neutrons (10¹⁵n/cm²) and 10⁸rad (Si) gamma rays with 1 MeV energy. In these harsh conditions, the variations of physical characteristic parameters were analysed. In ion implanted films, the coercive field increased from 0.3 to 0.4 oe after neutron irradiation. The gamma rays irradiation brought the strip width back to the value it had before the ion implant. The anisotropy field increased slightly (3%) under both irradiations. The decrease in operating margins of 64 K bit memory chips is presented and a good correlation is made with the previous results. These effects are explained by general phenomena describing the interaction between the irradiation and the material. These experiments show that bubble memories will only fail at a high level of neutron and gamma ray exposure.     

Effect of lanthanum on growth-induced anisotropy in LPE bubble garnet films

Growth-induced anisotropy, Ku, in bubble garnet films containing La and Eu or Sm has been found to be anomalous compared to that produced by Eu or Sm and smaller ions such as Y or Lu. In     

Automated spatial filtering for rapid characterization of LPE bubble garnet films

An automated spatial filtering apparatus used for characterization of magnetic bubble films with zero field strip widths greater than 1.5μm has been constructed. This apparatus makes measurements of the zero field period and the period in an applied magnetic field. When these two measurements are combined with measured values for the film thickness and the Neél temperature, values for relevant material parameters of the bubble films can be calculated using the Kooy and Enz theory. Details of the spatial filter apparatus, the method used for data analysis, and the accuracy of the method are discussed.     

Uniaxial and cubic anisotropy constants in ion-implanted Sm,Tm,Ga:YIG bubble thin films

The effects of ion implantation into (SmTmY)3(GaFe)5O12garnet thin films have been studied by ferromagnetic resonance. He+ ions were used for implantation with doses ranging from 3 to 4 × 10¹⁵He+/ cm²and implantation energy ranging from 150 to 175 Kev. The uniaxial and cubic anisotropy constants have been studied as a function of temperature from 0°C to 100°C for both as-grown and ion-implanted films. The implantation has effectively changed an easy-axis anisotropy to that of an easy plane in the implanted layers of the films. A cubic anisotropy constant K1with values varying from 4 × 10³to 6 × 10³erg/cm³at room temperature has been observed in these films. The results also indicated that to the first order, the implanted region in the film was essentially magnetically uncoupled from the bulk of the film.     

Stochastic generation accompanying parametric excitation of spin waves in yttrium iron garnet films

We report the results of experimental investigations of chaotic self-modulation of the envelope of surface spin waves as a result of first-order spin-wave parametric instability. The experimental apparatus consisted of a microwave oscillator with a spin-wave delay line in the feedback circuit. Pis’ma Zh. Tekh. Fiz. 24, 66–72 (April 12, 1998)     

Effects of annealing on propagation in ion-implanted contiguous-disk bubble devices

Bubble propagation margins are found to be affected by heat treatment in ion-implanted contiguous-disk devices fabricated on liquid-phase epitaxial (LPE) grown double-layer garnet films which support 1-μm bubbles. When an optical reflector is deposited directly on the driving layer interfacial diffusion takes place, and this raises the coercivity of the implanted layer, which in turn causes a severe degradation of propagation margins. In samples fabricated with optical reflectors isolated from the driving layer, the adverse effects of annealing on propagation margins are stronger in close-packed minor loops due to interaction of long-range charged walls as compared with isolated loops and isolated disks, and they cease to propagate bubbles after annealing in the temperature range of 350-400°C, whereas the loss of margins in the isolated loops and disks are typically less than 30 percent after 600-650°C annealing treatments. Stress gradients caused by the discontinuity in the overlay patterns contribute significantly to the increase of threshold drive field after anealing. The rapid degradation of propagation margins found after annealing in the temperature range of 350-400°C in all samples is caused by reordering of the damaged lattice.     

Determination of magnetic anisotropy constants for bubble garnet epitaxial films using field orientation dependence in ferromagnetic resonances

Cubic magnetocrystalline anisotropy constant K₁ as well as uniaxial anisotropy constant K_u and gyromagnetic ratio γ are precisely determined for (111) magnetic garnet epitaxial films from measurements on FMR field orientation dependence. Strict FMR conditions are derived from total free energy expressions, where the differences between magnetization direction and applied field direction are taken into consideration. By applying magnetic field in (110) plane, FMR is measured to obtain the three best fitting parameters of K₁, K_u and γ. Present analysis is compared with Cronemeyer et al's analysis. Influence of sample misalignment on measurement accuracy is also presented. Similarly, for (110) garnet films with orthorhombic magnetic anisotropy, measurements are carried out for two crystallographic planes of (001) and (110), and the four best fitting parameters of K₁, K_u, δ and γ are determined.     

Optical and luminescent properties of ion-implanted films

It has been shown that band parameters for unimplanted films differ from those for bulk materials. Mechanical stresses and increased concentrations of defects seem to be responsible for this difference. The neighbourhood of the surface and the existence of drain paths for bulk defects determine the activity of the surface as a collector for mobile defects and hence their accumulation and their subsequent combination and annihilation reactions. From this point of view ion-implanted films with radiation-induced defects exhibit specific types of behaviour. For example, low energy ion bombardment (together with the removal of a very thin surface layer by etching) leads to an extensive movement of defects towards the surface and to a purification of the corresponding layer. In a number of cases even structural phase transformations take place within the surface layer, which lead in particular to the creation of surface excitons.High energy ion bombardment does not alter the band parameters of the films at the depth d of ion penetration but distorts the structure at the surface owing to a drain of defects into this layer. At the same time centres of scattering and radiative recombination are effectively induced at the depth d.     

Depth distribution of ion-implanted argon in gadolinium and samarium films

The development of a model and theoretically evaluated distributions for impurities injected by ion bombardment into growing films are given. The influence of ion range distribution function, diffusion, impurity-defect interaction and film and substrate material differences upon the impurity concentration profiles is investigated. The possibility of uniform impurity distribution in the main part of the film with a sharp concentration gradient into the substrate is shown. The influence of diffusion leads to a decrease of gaseous impurity concentration in the film and penetration of impurities into the substrate; the relation of impurity diffusion coefficients and the segregation coefficient value is essential when the film and the substrate are made of different materials. Taking into account the trapping of impurities by defects we found that the distribution of the ‘free’ (mobile) impurities is inhomogeneous with a maximum near the growth boundary, this inhomogeneity is decreased with increased diffusion, while defect concentration increases. The concentration profiles of the trapped impurities (impurity-defect complexes) are very different, the complexes become distributed more homogeneously and the concentration of complexes increases as diffusion and the defect concentration increase.By use of secondary ion mass-spectrometry (SIMS) a distribution of ion-implanted argon through the film and part of the substrate depth was investigated as well as the distribution of the film and substrate materials themselves, using gadolinium and samarium films obtained by vacuum condensation on (100) molybdenum monocrystal under simultaneous 100 and 600 eV argon irradiation. The argon distribution through the film is found to be almost uniform with an exponential decrease in the substrate for gadolinium films at an energy of 100 eV. A considerable argon accumulation at the film-substrate boundary is found at an energy of 600 eV. For samarium films at an energy of 100 eV an anomalous argon and samarium penetration into the substrate as well as argon penetration into the layer deposited without irradiation of the film is obtained.     

Electrically controlled generator of micron and submicron water aerosol

A generator of micron and submicron water aerosol of combination (condensation and electrogasdynamic) type is described. In this generator, a steam-gas jet flowing via horizontal capillary from a container with supersaturated steam is subjected to the effect of corona discharge. Attention is called to the importance of taking into account the orientation of the capillary and position of the corona electrode relative to the steam-gas jet. It is found that the parameters of aerosol particles during the condensation of steam-gas jet significantly depend on the intensity of corona discharge. An explanation of observed phenomena is given within the assumption of competition between the forms of condensation in the steam-gas jet, namely, homogeneous condensation, heterogeneous condensation on ions of corona discharge, and heterogeneous condensation on water film fragments formed at the capillary exit section under the effect of electric field. The prevailing forms of condensation are determined in various modes of generator operation depending on the ambient temperature and the intensity of corona discharge.     

Observation of magnetic bubbles and structural transformation in amorphous garnet by electron microscopy

Magnetic bubbles have been observed in an amorphous garnet film obtained by vacuum deposition and annealed at 473K in air for complete oxidation. The bubbles are visible only in the amorphous state. When heated above 673K, the amorphous garnet film transforms into the crystalline phase accompanied by the disappearance of bubbles.     

Epitaxial growth experiments on SmLu- and EuLu-garnet films for the generation of magnetic bubble domains

Epitaxial growth of (SmLu)₃(FeAl)₅O₁₂ and (EuLu)₃(FeAl)₅O₁₂ films on the (111) plane of Gd₃Ga₅O₁₂ substrate has been studied with respect to relationships between melt composition and magnetic properties. A composition for bubble domains (2.5–8μm) has been defined experimentally, principally attained by changing the Al content in the melt. A lattice parameter for the mixed garnet can be expressed by a subtraction of 0.071 x (x = Al content in the film) from the interpolated lattice parameter for the garnet of end member. Growth induced uniaxial anisotropic energy (K_G) for SmLu-garnet (= 8022 erg/cm³) and for EuLu-garnet (= 10240 erg/cm³) exists in the films which have no lattice mismatch with the substrate. K_G decreases with an increasing of Al content (0.67 < x < 1.08 in atomic formula), whereas it is almost constant for SmLu-garnet.     

Stripe and bubble domains in CoCr films

Using the colloid-scanning-electron-microscope (SEM) method, an investigation was conducted of the domain structure of CoCr films (400-1740 nm thick) at different points of the hysteresis loop. In some cases, an AC field exceeding the value of the coercive force was applied in addition to the DC field. For low-coercivity samples (H_c/H_k~0.02) a bubble structure, which is energetically more favorable above a certain critical field, was observed. From the dependence of the bubble density on the DC field the value of the anhysteretic collapse field was estimated and compared with the theory. Attempts were made to observe the field dependence of the domain structure of high-coercivity samples (H_c/ H_k~0.08) with different thicknesses. For one sample the results were compared with those determined using the Kerr effect. For thicker films the colloid-SEM method permits the simultaneous observation of the magnetic domains and the columnar structure at the surface of the sample     

Decrease in work function of boron ion-implanted ZnO thin films

We have fabricated boron ion-implanted ZnO thin films by ion implantation into sputtered ZnO thin films on a glass substrate. An investigation of the effects of ion doses and activation time on the electrical and optical properties of the films has been made. The electrical sheet resistance and resistivity of the implanted films are observed to increase with increasing rapid thermal annealing (RTA) time, while decreasing as the ion dose increases. Without any RTA process, the variation of the carrier density is insensitive to the ion dose. With the RTA process, however, the carrier density of the implanted films increases and approaches that of the un-implanted ZnO film as the ion dose increases. On the other hand, the carrier mobility is shown to decrease with increasing ion doses when no RTA process is applied. With the RTA process, however, there is almost no change in the mobility. We have achieved the optical transmittance as high as 87% within the visible wavelength range up to 800 nm. It is also demonstrated that the work function can be engineered by changing the ion dose during the ion implantation process. We have found that the work function decreases as the ion dose increases.     

Linear birefringence control and magnetization in sputter-deposited magnetic garnet films

Birefringence control is essential in the fabrication of on-chip magnetooptic Faraday isolators. We report on film thickness and stress studies of birefringence in sputter-deposited single-layer bismuth-substituted iron garnet films and double-layer iron garnet films with gadolinium gallium garnet (GGG) covers. We examine compressively and tensilely strained films and analyze the photoelastic response of the sputter-deposited garnet films. We show that the net birefringence can be ed out under planar compressive strain conditions. Bilayer GGG on iron garnet film yields a reduced birefringence. Temperature control during the sputter deposition of the GGG cover is critical and strongly influences the magnetic moment and birefringence level in the waveguide. High-temperature deposition lowers the magnetization in the underlying iron garnet film.     

Determination of doses for ion implantation in garnet films

The effects of doses in implanted magnetic garnets are investigated by means of magnetic modifications of the implanted layer. Experiments performed on materials with various magnetostriction coefficients and with different growth induced anisotropies show that the stresses are proportional to the ion dose. At high dosage levels an elastic-plastic transformation occurs followed by a progressive destruction of the magnetic order. These results make possible the calculation of the dose necessary for a garnet, given its magnetostriction coefficient and its anisotropy energy.     

Growth and properties of garnet films for storage application

A discussion of the growth of garnet films by liquid phase epitaxy without rotation of the substrate is presented for magnetic garnet layers used as materials for bubble [(YSm)3(FeGa)5O12; (YLa)3(FeGa)5O12] and magneto-optical memories [(GdBi)3(FeGaAl)5O12]. The background of the experimental and compositional approach is given.     

Ellipsometric analysis of ion-implanted polycrystalline silicon films before and after annealing

A study of arsenic ion-implanted polycrystalline silicon films before and after annealing at various temperatures has been performed using spectroscopic ellipsometry in the ultraviolet to the visible spectral region. Using the Bruggeman effective medium approximation, an optical/structural model is presented for all the annealed samples explaining the measurements. Ellipsometric measurements reveal important structural changes as a function of annealing temperature which provide an interesting inside into the annealing kinetics of ion-implanted polycrystalline silicon films. This work also demonstrates the importance of spectroscopic ellipsometry in determining non-destructively the dielectric functions in materials that have undergone complex processing.     

The effects of spacing between garnet film and Permalloy overlay circuit in magnetic bubble devices

An experimental test set for magnetic bubble devices has been constructed in which the spacing between the garnet film and the Permalloy overlay is variable. The experimental uncertainty in spacing is approximatelypm.15mum, and spacings as small as.5mum have been attained. Bias margin data are presented which were taken at 1 Hz on a 20 micron period chevron circuit as a function of spacing. The collapse and strip-out fields begin to be affected when the spacing is comparable to the garnet film thickness, increasing as the spacing decreases. At larger spacing the high-bias failure mode changes from collapse to uncorrelated bubble motion. A theoretical model which accounts for some aspects of the spacing dependence of the strip-out and collapse fields is described. This model approximates the circuit by a continuous Permalloy sheet. At the low spacing required for efficient use of the rotating field, the model indicates that ±10% nonuniformity in a 2 micron spacing over the device area results in a degradation of the bias field operating range by about 12%.     

Laser annealing of gallium-substituted garnet epitaxial films in pressurized oxygen

The effects of laser annealing Ga-substituted EuYIG epitaxial films in still, controlled ambients of air and one to five atmospheres of pure oxygen have been studied. An approximately logarithmic increase in saturation magnetization (4pi M_{s}) and decrease in film magnetic Q factor were observed with increasing oxygen pressure in the annealing ambient. Compared with the most successful previous experiments, annealing at five atmospheres of oxygen displaced nearly twice the fraction of Ga from tetrahedral to octahedral lattice sites. As evidenced by the lack of film damage, the correlation of lattice parameter with the location of the Ga ions and the lack of broadening in the ferromagnetic resonance (FMR) lines, effective annealing temperatures above 1850K were achieved with no significant loss of oxygen from the films. The use of FMR to deduce the extent of film annealing was affirmed through the agreement of independent measurements of4piM_{s}by bubble statics and SQUID magnetometry in films indicated to be homogeneous by FMR.