We use the Kubo formalism to calculate the transresistivity ρ21 for carriers in coupled quantum wells in a large perpendicular magnetic field B. We find that ρ21 is enhanced by approximately 50-100 times over that of the B = 0 case in the interplateau regions of the integer quantum Hall effect. The presence of both electron-electron interactions and Landau quantization results in (i) a twin-peaked structure of ρ21(B) in the inter-plateau regions at low temperatures, and, (ii) for the chemical potential at the center of a Landau level band, a peaked temperature dependence of ρ21(T )/T 2 .

A treatment of frictional Coulomb drag between two two-dimensional electron layers in a strong perpendicular magnetic field, within the independent electron picture, is presented. Assuming fully resolved Landau levels, the linear response theory expression for the transresistivity 21 is evaluated using diagrammatic techniques. The transresistivity is given by an integral over energy and momentum transfer weighted by the product of the screened interlayer interaction and the phase space for scattering events. We demonstrate, by a numerical analysis of the transresistivity, that for well-resolved Landau levels the interplay between these two factors leads to characteristic features in both the magnetic field and the temperature dependence of 21 . Numerical results are compared with recent experiments. ͓S0163-1829͑97͒02640-4͔

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Signal degradation in spin-valve structures is today a concern for long-term stability of data storage devices. One of the possible degradation mechanisms of spin-valve structures in disk drive applications could be thermally activated diffusion between constituent layers. In order to predict and control performance degradation, the interdiffusion coefficients for all bilayers in the spin-valve structure will have to be determined. Here we report results from a Co90Fe10/Ru interface, common in many spin-valve structures. The diffusion in (0002) oriented polycrystalline Co90Fe10/Ru multilayers has been measured and quantified by x-ray reflectivity in the temperature range of 450–540 °C. The bulk diffusion in this case is described by an activation energy of Ea=4.95 eV and a prefactor of D0=6.43×10−9 m2/s. No grain boundary diffusion was detected in the large-grain structure dominated by high symmetry grain boundaries at the temperature interval in this study. For a spin-valve structure that contains Co90Fe10/Ru interfaces it is clear that with the absence of grain boundary diffusion and a very high activation energy to bulk diffusion degradation will first take place at another interface, or by another phenomenon.