We have fabricated arrays of high aspect ratio nickel columns in both PMMA and SiO2, and we have characterized their structure using transmission electron microscopy and scanning electron microscopy. We have also characterized the magnetics of the columns with magnetic force microscopy. Such characterization of high aspect ratio perpendicular magnetic particles is only rarely found in the literature. This work lays a foundation for further studies to test the viability of lithographically defined arrays of magnetic particles as an alternative high density storage medium.

Efficient inducement of bistable spin Hall effect using in-plane-magnetized V-shaped ferromagnetic wire Appl. Phys. Lett. 101, 082403 (2012) Practical system for the direct measurement of magneto-caloric effect by micro-thermocouples Rev. Sci. Instrum. 83, 083902 (2012) In situ measurement of alternating current magnetic susceptibility of Pd-hydrogen system for determination of hydrogen concentration in bulk Rev. Sci. Instrum. 83, 075102 (2012) Tunable magnetoelectric response of dimensionally gradient laminate composites Appl. Phys. Lett. 100, 212901 (2012) Tunable linear magnetoresistance in MgO magnetic tunnel junction sensors using two pinned CoFeB electrodes

The transition from traveling-wave to stationary convection in a binary-fluid mixture is studied as a function of Rayleigh number. The experiments are conducted in an annular container which provides periodic boundary conditions in the direction of the wave motion. In agreement with the predictions of recent theories, the transition is shown to be continuous with no measurable hysteresis. The functional dependence of the wave phase velocity on Rayleigh number is in agreement with the predictions over the entire traveling-wave branch.PACS numbers: 47.25.-c Convection in binary-fluid mixtures provides a model system with which to study a wide range of spatiotemporal behavior. In experiments with ethanol-water mixtures, as the temperature difference across the fluid layer is increased, the conducting (motionless) state undergoes a Hopf bifurcation to a state of traveling-wave (TW) convection. For the parameter range of interest, this Hopf bifurcation is subcritical, and the linear convecting state grows into a large-amplitude nonlinear TW state before saturating. A wide variety of nonlinear phenomena have now been studied in this system, including the competition of counterpropagating traveling waves, stable fronts separating conduction and convection, and the dynamics of spatiotemporal defects. 1 " 3 Recently, nonlinear theories have been developed 4,5 and numerical calculations performed 6 to describe this large-amplitude TW state. This Letter reports experiments which directly test the predictions of these theories. The agreement between theory and experiment indicates that we now understand the nature of the uniform TW state in this system.In a binary-fluid mixture the separation ratio y/, which is proportional to the Soret coefficient, parametrizes the concentration-driven fluid density changes. ] For y/ < 0, the lighter component diffuses toward the colder region, thereby stabilizing the fluid layer against convection, and the Rayleigh number at onset is larger than that for a pure fluid. In this Letter all Rayleigh numbers r will be normalized by the onset Rayleigh number R c of convection in a pure fluid with the same thermal properties as the mixture; thus r = R/R c > 1.At the onset of convection, the convective amplitude is observed to grow via a long transient to a state of slowmoving traveling waves; 7 at if/--0.25 the frequency is a factor of 30 lower than the Hopf frequency (coo). If the Rayleigh number is then reduced, this state of nonlinear traveling waves remains stable down to a saddlenode bifurcation back to conduction at r s . Numerical calculations indicate that the linear concentration profile present in the conduction state is destroyed by convective mixing in the TW state. 8 Thus, the vertical concentration gradient remains only in thin, horizontal boundary layers at the top and bottom of the fluid layer, and the fluid is well mixed in the interior of the rolls. Concentration from these boundary layers is fed into the upflow and downflow boundaries between the rolls, forming a lateral concen...

No abstract

No abstract