A self-contained magnetic bubble-domain memory chip

All the functions essential for the operation of a memory (viz., storage, access, write, read, and detection) can be performed within a bubble-domain memory chip. This enables the design of a memory with a minimum number of peripheral circuits and interconnections, and a short access time. It is conceivable to achieve a 10⁶-bit memory with fewer than 20 circuits (and interconnections), and with a few hundreds of microseconds access time. The present paper describes the devices required to implement such a memory, experimental data to demonstrate the operability of such devices, and the design criteria.     

Combined X-ray microdiffraction and topography experiment for microstructural analysis of heterogeneous materials

A new experimental set-up combining X-ray topography and microbeam diffraction has been designed for the investigation of heterogeneous microstructures with features in the size range of more than 50m. Built around a four-circle goniometer of 5/1000° angular resolution, this apparatus offers similar facilities to those obtained by TEM but at a different scale. In the Berg-Barrett position, grain and subgrain boundaries can be observed over large surface areas (typically 100 mm²). Based on topography observations, areas of interest of typically 100m diameter can be precisely selected for microdiffraction measurements. A laser beam directed through the pinhole system of the X-ray microbeam collimating system permits one to directly visualize the irradiated zone. The divergence of the X-ray microbeam is typically 0.034° (full width at half maximum) and permits the measurement of lattice spacing variations (a/a) of the order of 10^–4. While TEM permits one to examine very localized areas, this new device is appropriate to detect long-distance effects and phase interactions in materials with coarse distributed heterogeneities. In order to demonstrate the versatility of this new device, the orientation distribution, variation of lattice spacing and mosaic structure of dendrites in directionally solidified nickel-base alloys are analysed.     

Flux growth and characterization by X-ray topography of rare earth arsenates

Optically clear crystals of rare earth arsenates, RAsO₄, have been grown from Pb₂As₂O₇ flux by slow cooling and recovered by a hot-pouring technique. X-ray anomalous transmission topography has shown that the crystals are of good quality, and their perfection is compared with that of RVO₄ crystals grown by a similar method. The surfaces of crystals recovered by hot-pouring were found to contain higher densities of precipitates than those recovered by dissolution of the flux.     

Measurement of surface topography of magnetic recording materials through computer analyzed microscopic interferometry

A recently developed surface characterization technique, Computer Analyzed Microscopic Interferometry, is shown to have many applications in the study of magnetic recording surfaces. Three-dimensional and quantitative interferometric images produce very high depth resolution without reducing the field of view. This allows very precise surface roughness and volume measurements.     

X-ray topography of hydride domains

X-ray topographic techniques were applied to the study of twin related domains in niobium hydride and deuteride crystals. It was shown that contrast between the domains, which results from small differences in orientation, allows the method to be used in the study of the domain behavior. The method is compared to the alternate technique of optical metallography.     

Preparation and characterization of iron phthalocyanine polymer magnetic materials

A novel kind of polymer magnetic material iron phthalocyanine (FePc) was prepared via the polymerization of phthalonitrile with iron pentacarbonyl. The pre-polymerization was monitored by FTIR and UV–Vis spectra. Microwave dielectric properties of prepolymers were dependent on their chemical structures. The thermal properties of FePc polymer were evaluated by TGA, the initial decomposition temperature of completely cured polymer was about 420 °C and char yield at 800 °C was 63.56%. Controlling the pre-polymerization degree of phthalonitrile by the reaction time, the magnetic properties of cured polymer materials can be finely tuned. The saturation magnetization of cured polymer decreased from 2.48 to 0.42 emu/g, whereas the coercive force increased from 123.8 to 228.6 Oe. The microstructure of iron phthalocyanine polymer was characterized by scanning electron microscope and the typical layer structure morphology of phthalocyanine polymer was clearly observed.     

X-ray surface reflection and transmission topography of magnetic domain walls in Czochralski-grown nickel single crystals

Ferromagnetic domain walls are observed in large Czochralski-grown nickel single crystals by X-ray double crystal diffraction topography in the surface reflection geometry as well as in the transmission geometry. The images of magnetic domain walls in surface reflection topographs possess almost as good contrast as those in transmission topographs, and even reveal fine detailed structure. Based on preliminary arguments, the images observed in the surface reflection topographs are attributed to 180° walls intersecting the crystal surface obliquely, while the transmission topographs easily image 71° and 109° walls in the interior of the crystals.     

Preparation and characterization of multifunctional magnetic mesoporous calcium silicate materials

Abstract

We have prepared multifunctional magnetic mesoporous Fe–CaSiO₃ materials using triblock copolymer (P123) as a structure-directing agent. The effects of Fe substitution on the mesoporous structure, in vitro bioactivity, magnetic heating ability and drug delivery property of mesoporous CaSiO₃ materials were investigated. Mesoporous Fe–CaSiO₃ materials had similar mesoporous channels (5–6 nm) with different Fe substitution. When 5 and 10% Fe were substituted for Ca in mesoporous CaSiO₃ materials, mesoporous Fe–CaSiO₃ materials still showed good apatite-formation ability and had no cytotoxic effect on osteoblast-like MC3T3-E1 cells evaluated by the elution cell culture assay. On the other hand, mesoporous Fe–CaSiO₃ materials could generate heat to raise the temperature of the surrounding environment in an alternating magnetic field due to their superparamagnetic property. When we use gentamicin (GS) as a model drug, mesoporous Fe–CaSiO₃ materials release GS in a sustained manner. Therefore, magnetic mesoporous Fe–CaSiO₃ materials would be a promising multifunctional platform with bone regeneration, local drug delivery and magnetic hyperthermia.     

X-ray topography for fractography of single-crystal components

X-ray diffraction topography is a new tool that may help fractographic analysis of single-crystal structural materials. It is sensitive to local strain and/or crystallographic orientation and provides a unique view of single-crystal samples both before and after fracture. It can find strength-and performance-limiting surface and subsurface flaws that are undetectable by other methods or are detectable only with great difficulty and provides a complementary view of the fracture surface. The attributes of synchrotron-based X-ray topography as applied to fractography are described and illustrated with examples from recent experiments on sapphire.     

Microwave characterization of magnetic materials under uniaxial andbiaxial mechanical compressive stress

A new technique of determining the permittivity and the permeability of ferrite material from microwave measurements in a rectangular waveguide under biaxial mechanical stress is presented. Three measuring cells, corresponding to the application of uniaxial and biaxial compressive forces are developed, each in the range of 2.6 GHz to 3.95 GHz, and 3.95 GHz to 5.85 GHz. Measurements of the permittivity and the permeability of a sample of nickel-zinc ferrite are performed under stress levels up to 60 MPa. The results show that the permittivity remains isotropic and does not depend on the level of stress, and that the permeability is affected by the magnitude and direction of the stress applied     

Global characterization of soft magnetic materials under rotating flux density conditions

Although several authors have proposed different devices to measure the iron loss in magnetic sheets used in the building of electrical machines, few of them take into account the real electromagnetic working context. This paper deals with the possibility of determining the iron loss and the apparent magnetic permeability from the measurement of the flux density in the air gap with the use of the Maxwell's tensor and an analog computer. We propose new methods to obtain the power loss and the magnetic permeability of magnetic samples.     

Metrological characterization of X-ray diffraction methods for determination of crystallite size in nano-scale materials

Crystallite size values were determined by X-ray diffraction methods for 210 TiO₂ (anatase) nanocrystalline powders with crystallite size from 3 nm to 35 nm. Each X-ray diffraction pattern was processed using different free and commercial software. The crystallite size calculations were performed using Scherrer equation and Warren–Averbach method. Statistical treatment and comparative assessment of the obtained results were performed for the purpose of an ascertainment of statistical significance of the obtained differences. The average absolute divergence between results obtained with using Scherrer equation does not exceed 0.36 nm for the crystallites smaller than 10 nm, 0.54 nm for the range 10–15 nm and 2.4 nm for the range > 15 nm. We have also found that increasing the analysis time improves statistics, however does not affect the calculated crystallite sizes. The values of crystallite size determined from X-ray data were in good agreement with those obtained by imaging in a transmission electron microscope.     

The static M-H loops of stressed magnetic materials with intergranular interaction

A model for low frequency rotational switching of the magnetization in magnetic materials, leading to individualM-Hcurves, is given. Magnetocrystalline and stress induced anisotropy energies are averaged under the assumption of strong intergranular interaction. Consideration is given to the manner in whichM-Hcurve characteristics are related to such factors as crystallite orientation, mechanical stresses, and material constantsK_{1}, lambda_{100}, and λ111.     

Thermodynamics of deformable magnetic materials with memory

The theory of deformable heat conducting magnetic materials with fading memory is developed. The case of saturated ferrogmagnetic type materials is treated in detail. The restrictions placed on the response functionals by the Clausius-Duhem inequality are derived. Relaxation is discussed and integrated dissipation inequalities are derived. Finally, the theory of deformable paramagnetic materials with memory is briefly developed.     

Application of X-ray refraction topography to fibre reinforced plastics

The effect of X-ray refraction employs an unconventional small angle X-ray scattering (SAXS) technique which has been developed and applied to meet actual problems for improved non-destructive characterisation of advanced materials. The X-ray refraction technique makes use of X-ray optical effects at micro interfaces of composite materials. This method reveals the inner surface and interface concentrations in nanometer dimensions due to the short X-ray wavelength near 10⁻⁴ μm. Sub-micron crack and pore sizes are easily determined by “X-ray refractometry” without destroying the structure by cutting or polishing for microscopic techniques. The non-destructive characterisation of microfailure e.g. voids, fibre debonding, fibre cracks and microcracks of a short glass fibre reinforced polyoximethylene (POM-GF) after mechanical loading and accelerated ageing is investigated. X-ray refraction topographs are illustrated, showing the damage accumulation of POM-GF specimens after the fatigue test.     

X-ray diffraction topography of deformation accompanying laser drilling of silicon

X-ray diffraction topography was used to study laser drilling of (001) silicon. Double crystal, Lang projection and section topography were used to characterize the deformation surrounding holes drilled with a Nd/YAG laser operated at various energy densities. Scanning electron microscopy showed significantly different hole wall morphologies, and the relationship between these structures and the resulting strain field was investigated. This preliminary study indicated the feasibility of using section topography to quantify and map the different components of strain around laser-drilled holes in silicon.     

Nondestructive characterization of materials with variable properties

Summary Materials with continuous variable properties in time and space are considered. The possibility of nondestructive characterization of these materials on the basis of nonlinear longitudinal wave propagation data is discussed on the basis of recent results. The model direct and inverse problems are solved. The utilization of obtained results enables one to solve several nondestructive material characterization problems.