We have measured coercive field and switching voltage versus thickness in PbZr0.54Ti0.46O3 thin (0.15–0.50 μm) films, together with switching times and current transient shapes versus field and temperature. The results show activation fields of order 120 kV/cm at room temperature, threshold voltages below 1.3 V, and switching speeds faster than 100 ns, demonstrating that fast, nonvolatile memories can be constructed that are compatible with standard silicon or GaAs integrated circuit voltage levels, without the need for an internal voltage pump. The displacement current transient data yield 2.5 as the dimensionality of domain growth if one-step intial nucleation rate is assumed, and are compatible with the theory of Ishibashi, yielding imaxtmax/Ps=1.65±0.23, in comparison with the predicted 1.646. The switching time exhibits an activation field dependence upon both voltage and temperature through a single reduced parameter (TC−T)(VTC),−1 in accord with the theory of Orihara and Ishibashi.
We report a large spin-polarized current injection from a ferromagnetic metal into a nonferromagnetic semiconductor, at a temperature of 100 Kelvin. The modification of the spin-injection process by a nanoscale step edge was observed. On flat gallium arsenide [GaAs(110)] terraces, the injection efficiency was 92%, whereas in a 10-nanometer-wide region around a [111]-oriented step the injection efficiency is reduced by a factor of 6. Alternatively, the spin-relaxation lifetime was reduced by a factor of 12. This reduction is associated with the metallic nature of the step edge. This study advances the realization of using both the charge and spin of the electron in future semiconductor devices.
We have performed Brillouin studies of acoustic-phonon behavior in barium sodium niobate above and below its phase transition at To --105 K. Anomalies in sound velocity and attenuation are observed for the sound waves corresponding to the Cll and C22 elastic coefficients. Above To the sound-ve1ocity anomalies display lambda-shaped dips af algebraic form V~~( T) = V~(oo ) -P/(T -Tc), with Tc several degrees lower than the actual transition temperature To, this is the form expected for free energies dominated by linear coupling between strain and the order parameter. Below To, V~&(T)= V&(00) P'/(T-, ' -T). The attenuation displays an increase of approximately 100% as the transition temperature is approached from above or below. By combining sound-velocity and attenuation data through a Landau-ghalatnikov approach, we are able to extract a single relaxation time and find that this time~satisfies the expected mean-field dependence
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