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We determined the spin-transport properties of Pd and Pt thin films by measuring the increase in ferromagnetic resonance damping due to spin-pumping in ferromagnetic (FM)-nonferromagnetic metal (NM) multilayers with varying NM thicknesses. The increase in damping with NM thickness depends strongly on both the spin- and charge-transport properties of the NM, as modeled by diffusion equations that include both momentum- and spin-scattering parameters. We use the analytical solution to the spin-diffusion equations to obtain spin-diffusion lengths for Pt and Pd. By measuring the dependence of conductivity on NM thickness, we correlate the charge- and spin-transport parameters, and validate the applicability of various models for momentum-scattering and spin-scattering rates in these systems: constant, inverse-proportional (Dyakanov-Perel), and linear-proportional (Elliot-Yafet). We confirm previous reports that the spin-scattering time appears to be shorter than the momentum scattering time in Pt, and the Dyakanov-Perel-like model is the best fit to the data. [ABSTRACT FROM AUTHOR]

Motivated by the importance of magnetization dynamics in nanomagnets for the development and optimization of magnetic devices and sensors, we measured and modeled spin wave spectra in patterned elliptical nanomagnets. Ferromagnetic resonance spectra for multiple nanomagnets of Ni80Fe20, fabricated by electron-beam lithography to have nominal short-axes of 200 nm or 100 nm, were measured by use of heterodyne magneto-optical microwave microscopy. Scanning electron microscope images taken of the same nanomagnets were used to define element shapes for micromagnetic simulations. The measured spectra show significant differences between nominally identical nanomagnets, which could be only partially attributed to uncontrolled shape variations in the patterning process, as evidenced by the limited agreement between the measured and simulated spectra. Agreement between measurements and simulations was improved by including a zone of reduced magnetization and exchange at the edges of the nanomagnets in the simulations. Our results show that the reduction of shape variations between individual magnetic random-access memory elements can potentially improve their performance. However, unambiguous determination of materials parameters in nanomagnets based on analysis and modeling of spin wave spectra remains problematic. [ABSTRACT FROM AUTHOR]

The spin dynamics of sub-100-nm Ni80Fe20 nanomagnets are directly measured using the magneto-optic Kerr effect and a broadband detection scheme. Elliptical dots approximately 68 nm in diameter and 10 nm thick were fabricated in 20×20 μm2 arrays. There is approximately a factor of 2 increase in the effective linewidth when compared to a 20 μm diameter continuous disk of the same material. Using micromagnetic simulations, we model the effect of dot-to-dot size variation on the effective linewidth and find that 2 nm size variations are more than sufficient to account for the effective increase in linewidth. [ABSTRACT FROM AUTHOR]

A single monolayer (ML) of Cr was found to have a significant effect on the magnetic properties of subsequently deposited ultra-thin epitaxial Co layers. Brillouin light scattering (BLS) indicated that the Cr interlayer reversed the sign of the interface contribution to the total perpendicular magnetic anisotropy (PMA) of the Co. The negative value of the interfacial anisotropy term implied in-plane behavior. As a result, the samples with Cr became in-plane at about 11 ML of Co (1 ML of Co is about 0.2 nm), but the structures without Cr, while behaving qualitatively similar, exhibited higher total PMA and became in-plane at about 13 ML of Co. This behavior was also confirmed using perpendicular magneto-optic Kerr effect measurements. These results suggested that the in-plane nature of the interface anisotropy term for those samples with Cr was significant in determining their greater sensitivity to increased Co thickness. The impact of interdiffusion at the Cr/Co interface should not be neglected; by itself Cr is antiferromagnetic, and as an additive to Co and with no diffusion to grain boundaries (these films are single crystal), a greater effect from it is expected than from simple diluents such as Cu or Au. A monotonic decrease in magnetization with decreasing Co thickness was observed, but only for the samples with Cr, further suggesting the importance of interdiffusion. [ABSTRACT FROM AUTHOR]

The development and baseline operation of an acoustic view cell for observing fluids, and fluid-fluid and fluid-solid interfaces in porous media over the frequency range of 10-5000 Hz is described. This range includes the industrially relevant frequency range 500-5000 Hz that is not covered by existing devices. Pressure waveforms of arbitrary shape are generated in a 17.46 mm ID by 200 mm and 690.5 mm long glass tubes at flow rates up to 200 ml/min using a syringe pump. Peak-to-peak amplitudes exceeding 80 kPa are readily realized at frequencies from 10 to 5000 Hz in bubble free fluids when actuated with 20 Vpp as exemplified using castor oil. At resonant frequencies, peak-to-peak pressure amplitudes exceeding 500 kPa were obtained (castor oil at 2100 Hz when actuated with 20 Vpp). Impacts of vibration on macroscopic liquid-liquid and liquid-vapour interfaces and interface movement are illustrated. Pressure wave transmission and attenuation in a fluid saturated porous medium, randomly packed 250-330 μm spherical silica beads, is also demonstrated. Attenuation differences and frequency shifts in resonant peaks are used to detect the presence and generation of dispersed micro-bubbles (<180 μm diameter), and bubbles within porous media that are not readily visualized. Envisioned applications include assessment of the impacts of vibration on reaction, mass transfer, and flow/flow pattern outcomes. This knowledge will inform laboratory and pilot scale process studies, where nuisance vibrations may affect the interpretation of process outcomes, and large scale or in situ processes in aquifers or hydrocarbon reservoirs where imposed vibration may be deployed to improve aspects of process performance. Future work will include miscible interface observation and quantitative measurements in the bulk and in porous media where the roles of micro-bubbles comprise subjects of special interest. [ABSTRACT FROM AUTHOR]

Two parallel multi-element ultrasonic acoustic arrays combined with sets of focal laws for acoustic signal generation and a classical tomographic inversion algorithm are used to generate real-time two-dimensional micro seismic acoustic images of multiphase materials. Proof of concept and calibration measurements were performed for single phase and two phase liquids, uniform polyvinyl chloride (PVC) plates, and aluminum cylinders imbedded in PVC plates. Measurement artefacts, arising from the limited range of viewing angles, and the compromise between data acquisition rate and image quality are discussed. The angle range of scanning and the image resolution were varied, and the effects on the quality of the reproduction of the speed of sound profiles of model solids and liquids with known geometries and compositions were analysed in detail. The best image quality results were obtained for a scanning angle range of [-35°, 35°] at a step size of 2.5° post processed to generate images on a 40 µm square grid. The data acquisition time for high quality images with a 30 mm x 40 mm view field is 10 min. Representation of two-phase solids with large differences in speed of sound between phases and where one phase is dispersed in the form of macroscopic objects (greater than 1 mm in diameter) proved to be the most difficult to image accurately. Liquid-liquid and liquid-vapor phase boundaries, in micro porous solids by contrast, were more readily defined. Displacement of air by water and water by heptane in natural porous limestone provides illustrative kinetic examples. Measurement results with these realistic cases demonstrate the feasibility of the technique to monitor in real time and on the micrometer length scale local composition and flow of organic liquids in inorganic porous media, one of many envisioned engineering applications. Improvement of data acquisition rate is an area for future collaborative study. [ABSTRACT FROM AUTHOR]

Speed of sound and acoustic wave attenuation are sensitive to fluid phase composition and to the presence of liquid-liquid interfaces. In this work, the use of an acoustic array comprising 64 elements as a non-intrusive sensor for liquid-liquid interface, phase separation kinetics measurement in bulk fluids, and local composition measurement in porous media is illustrated. Three benchmark examples: the phase behaviour of methanol + mixed hexanes and methanol + heptane mixtures at 25.0 °C and 1 bar, and Athabasca bitumen + heptane in a synthetic silica porous medium at 22.5 °C and 1 bar, illustrate the accuracy of liquid-liquid interface and potential research and industrial applications of the technique. Liquid-liquid interfaces can be detected independently using both speed of sound and acoustic wave attenuation measurements. The precision of the interface location measurement is 300 μm. As complete scans can be performed at a rate of 1 Hz, phase separation kinetics and diffusion of liquids within porous media are readily tracked. The technique is expected to find application where the fluids or porous media are opaque to visible light and where other imaging techniques are not readily applied, or are too costly. A current limitation is that the acoustic probes must be cooled to less than 315 K in order for them to operate. [ABSTRACT FROM AUTHOR]

We studied the microwave assisted magnetic reversal of 65×71 nm2 elliptical Ni80Fe20 nanomagnets. Hysteresis curves were measured by magneto-optical Kerr effect for a range of microwave frequencies and amplitudes. The coercive field Hc was reduced by 26% for an rf field of 0.08Hc when the microwave frequency coincided with the minimum of the experimentally determined ferromagnetic resonance frequency with varying dc field. The experimental results for the fractional reduction in Hc with rf field amplitude are in good agreement with numerical simulations for an array of interacting macrospins with a physically realistic shape anisotropy distribution. [ABSTRACT FROM AUTHOR]

Dynamic wavelength stabilization of an AlGaAs diode laser has been demonstrated. The diode laser is butt coupled to a stripe-loaded optical waveguide which contains a Bragg reflecting grating. The laser is pulsed with 50-ns-long, 25% duty cycle, 100% modulation depth pulses and the waveguide output is observed to remain at single wavelengths over a peak current range of 120-160 mA and 15 °C temperature variations. [ABSTRACT FROM AUTHOR]

Previous work has indicated that there may be a positive relationship between the duration and extent of breath intake and the length of an upcoming utterance. However, none of that work has been free of alternative interpretations. An attempt was made to avoid some of those by forcing subjects to utter single sentences ranging in length from 5 to 82 syllables (mean of 27), after inspiring fully and then expiring down to a set level before uttering the sentence. For three subjects, there was a significant positive relationship between breath intake and utterance length (0.65, 0.50, and 0.29 individually). This was still true without those utterances containing a secondary breath (0.53, 0.54, and 0.29). The two subjects with the higher correlations also exhaled more quickly for the shorter sentences than longer ones. The other subject had no correlation with exhalation rate: He might have been selecting a point within a rather large range of starting lung volumes, with only the longest sentences requiring that the range's lower part be avoided. The individual differences need further investigation, but there is a correlation between the duration of the sentence to be said and the breath before it. [Work supported by NIH Grant No. HD-01994.] [ABSTRACT FROM AUTHOR]