The propagation of magnetic bubbles on permalloy disks

A magnetic bubble generator consisting of a Permalloy disk and a current conductor loop has been used recently in a mass memory design utilizing magnetic bubble technology. The bias field range in which the disk can hold the seed bubble is measured in this report as a function of of the rotating field frequency. Above a critical frequency fc, the bias field margins begin to decrease. The dependence of fcon disk size is obtained for disks with diameters from 16 μm up to 43 μm at rotating fields of 20 and 30 Oe. The separation between Permalloy disks and the garnet film is kept at 0.8 μm or 1.6 μm. Results show that at a fixed rotating field, a smaller disk is preferable at higher frequency for a magnetic bubble material with a given mobility. The critical frequency fcobtained is in good agreement with a theoretical calculation using the viscous damping model by Rossol et al. For frequencies below fc, the bias field margin on the disk is equal to that of the propagating channel and circuit failure due to the loss of the generator seed bubble can be eliminated.     

Modeling of crack propagation in strengthened concrete disks

Crack propagation in strengthened concrete disks is a problem that has not yet been addressed properly. To investigate it, a cracked half-infinite disk of concrete is strengthened with a linear elastic material bonded to the surface, and analyzed using two different finite element modeling approaches. The first method is 3D modeling of strengthening, interface and disk, and the second method is modeling of an equivalent disk in 2D, with an effective cohesive crack, equivalent thickness and equivalent stiffness. The 2D modeling approach simplifies modeling of the problem significantly and reduces the computational efforts and time. A good prediction of the cracking response, global response and load was obtained with the 2D model, whereas prediction of the size and shape of the interface debond was only approximate. It is concluded that the effective cohesive modeling approach can be used instead of 3D calculations to predict the response of a structure and that it opens up for simpler evaluation of strengthened concrete structures using the finite element method.     

Bubble domain propagation dynamics in field-access permalloy driving circuits

To improve the understanding of the bubble domain propagation a stroboscopic investigation of bubble displacement with a permalloy T-bar overlay was undertaken at various values of drive field rotation rate. In addition to stepwise change of bubble wall velocity, variation distortion of the bubble shape in the process of propagation and an asynchronous lag of the bubble relative to the drive field vector were also observed, the lag increasing with the rotation rate. To explain these results a simplified method for determining the bubble position in a magnetostatic well was proposed whereby elements of the permalloy overlay was divided into elementary rectangular components. The computed data are in good agreement with the experimental findings and this permits explanation of a number of phenomena observed in bubble circuits.     

离子注入制备GaAs:Mn薄膜的性质研究

采用高能离子注入的方式,在半绝缘性的GaAs衬底中掺杂引入Mn离子制备了磁性半导体.借助于X-射线衍射仪(XRD)进行了结构分析,没有发现新的衍射峰,并运用高分辨率X射线衍射仪(HR-XRD)分析了Mn离子注入后衬底(004)峰的微小变化.根据原子力显微镜的结果发现,注入后的样品表面没有发生明显的变化.通过使用超导量子干涉仪SQUID进行变温分析,在所分析范围内M-T曲线存在拐点,但其所对应的铁磁性转变温度低于室温.     

室温铁磁性GaN:Cr薄膜的性质研究

采用高能离子注入的方式,在GaN衬底中掺杂引入Cr离子制备了磁性半导体.借助于X射线衍射仪(XRD)进行了注入前后结构的对比分析,没有发现新的衍射峰,并运用高分辨率X射线衍射仪(HR-XRD)分析了Mn离子注入后衬底(0002)峰的微小变化.根据原子力显微镜的结果,发现注入后的样品表面起伏比较大,发生明显的变化.通过使用超导量子干涉仪SQUID进行变温分析,在所分析的10～300K范围内,磁化强度变化幅度较小,样品在室温条件下仍然保持铁磁性.     

Bubble circuit fabrication by electrodeposition

Bubble domain memory chips with micron dimension patterns have been fabricated by additive electroplating through photoresist windows using the conductor first processing. Etching defines the detector strips and removes the plating base. The various fabrication steps are described and discussed. The uniformity of the plated films is good and gives a reasonable yield. Nonmagnetic underlayers were plated below the NiFe bars. The gap width could be reduced by overplating the photoresist windows. 4 kbit chips have been fabricated with the processes described.     

Modification of the gas-separating properties of ion-implantation polymer membranes

We have studied the gas-separation properties of industrial polyvinyltrimethylsilane (PVTMS) membranes, as well as of experimental specimens of polyarylate siloxane, modified with ions C⁺, Ar⁺, B⁺, and N⁺.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 57, No. 6, pp. 888–892, December, 1989.     

水底爆炸气泡脉动特性

为研究水底爆炸气泡脉动特性,采用PAMFLOW软件和基于JWL状态方程的气泡脉动计算程序对水底爆炸气泡脉动特性进行了数值计算,并用经验公式对自由水域爆炸气泡脉动特性进行了计算.计算结果表明水底爆炸在整个气泡运动过程中,气泡的中心向海底贴附,并形成指向海底的高速射流,气泡被压扁;水底爆炸的气泡膨胀半径大于在无限水域中爆炸;2种数值计算结果比较吻合,且与经验公式计算结果相符,说明采用这2种数值计算方法来研究水底爆炸气泡脉动特性合理.     

Method for fast-switching the ion beam in an ion-implantation facility

The accuracy to which a desired dopant concentration can be attained through ion implantation depends largely upon the time constant for switching the ion beam on and off. Different means for switching the ion beam are discussed and a fast-switching device is described. The new device allows for a switching time constant of about 2 ms. During the switching process, no ions of other species can reach the target.     

Three-dimensional holographic disks

We describe optical disks that store data holographically in three dimensions by using either angle multiplexing or wavelength multiplexing. Data are stored and retrieved in parallel blocks or pages, and each page consists of approximately 10(6) bits. The storage capacity of such disks is derived as a function of disk thickness, pixel size, page size, and scanning parameters. The optimum storage density is approximately 120 bits/μm(2).     

High-resolution imaging of ion-implantation damage and mechanism of amortization in semiconductors

We have investigated the atomic structures of displacement cascades and amorphous-crystalline interfaces in silicon, ion implanted at 4 K, using high-resolution electron microscopy. The nature of the cascades and the process of amorphization are shown to be strong functions of ion-implantation and substrate variables. At 4 K the specific damage energy density for the crystalline to amorphous phase transition in silicon has been determined to be 12 eV/atom. The details of atomic structures of amorphous silicon and amorphous-crystalline interfaces are presented. The calculations of the mean free path between collisions and the energy deposited per atom are found to be consistent with experimental observations on amorphization of silicon.     

Numerical analysis of ion-implantation in target with a rectangular groove

Ion dynamics of pulsed plasma sheath during the plasma source ion-implantation (PSII) affects the resultant surface properties and structures. In this work, a two-dimensional fluid model is applied to the problem of computing ion dynamics in the sheath of a target with a rectangular groove. The evolution of sheath edge, x and y components of ion velocity on the target surface are simulated to describe the physics of sheath in PSII.     

Carbon nanofoam formed by laser ablation

Foam-like carbon (carbon nanofoam, CNF) which belongs to the porous carbon family is formed by pulsed laser ablation of graphite in liquid nitrogen. Each bubble is about 3-10 nm in size and has a layered structure with typically one to four graphene layers. The CNF forms nanoparticles of about 100 nm in size. CNF encapsulating platinum nanoparticles (Pt@CNF) is formed when a mixture of graphite, platinum, and hexadecanoic acid is used as a target. Each bubble encapsulating a platinum nanoparticle is approximately 15 +/- 4 nm in diameter and contains typically 6 +/- 3 graphene walls. The platinum nanoparticles in the CNF are 9 +/- 4 nm in diameter. The annealing of the Pt@CNF at 300 degrees C for a week in vacuum reveals that the CNF effectively prevents the platinum nanoparticles from aggregating.     

Bubble cutting circuits

An inhomogeneous applied field can cause an instability in a strip domain that can be used for the controlled generation of bubble domains. These instabilities have been studied experimentally and theoretically by means of a variational calculation. Good agreement is obtained between wall shape calculations and experimental data. Predictions of cutting current as a function of strip width deviate, however, for widths larger than ∼5.5h due to the limitations of the model and the experimental conditions.     

A new route toward semiconductor nanospintronics: highly Mn-doped GaAs nanowires realized by ion-implantation under dynamic annealing conditions

We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.