Resistance of multilayers with long length scale interfacial roughness

The resistance of multilayers with interface roughness on a length scale which is large compared to the atomic spacing is computed in several cases via the Boltzmann equation. This type of roughness is common in magnetic multilayers. When the electronic mean free paths are small compared to the layer thicknesses, the current flow is non-uniform, and the resistance decreases in the Current-Perpendicular-to-Plane (CPP) configuration and increases in the Current-In-Plane (CIP) configuration. For mean free paths much longer than the layer thicknesses, the current flow is uniform, and the resistance increases in both the CPP and CIP configurations due to enhanced surface scattering. In both the CPP and CIP geometries, the giant magnetoresistance can be either enhanced or reduced by the presence of long length scale interface roughness depending on the parameters. Finally, the changes in the CPP and CIP resistivities due to increasing interface roughness are estimated using experimentally determined parameters.Comment: 15 pages, 10 figure

Calculation of Giant Magnetoresistance in Laterally Confined Multilayers

We have studied the Giant Magnetoresistance (GMR) for laterally confined multilayers, e.g., layers of wires, using the classical Boltzmann equation in the current-in-plane (CIP) geometry. For spin-independent specularity factors at the sides of the wires we find that the GMR due to bulk and surface scattering decreases with lateral confinement. The length scale at which this occurs is of order the film thickness and the mean free paths. The precise prefactor depends on the relative importance of surface and bulk scattering anisotropies. For spin-dependent specularity factors at the sides of the wires the GMR can increase in some cases with decreasing width. The origin of the change in the GMR in both cases can be understood in terms of lateral confinement changing the effective mean free paths within the layers.Comment: 18 pages, 7 figure

Correlation between Spin Polarization and Magnetic Moment in Ferromagnetic Alloys

The correlation between the magnetic moment in ferromagnetic alloys and the tunneling spin polarization in ferromagnet-insulator-superconductor tunneling experiments has been a mystery. The measured spin polarization for Fe, Co, Ni, and various Ni alloys is positive and roughly proportional to their magnetic moments, which can not be explained by considering the net density of states. Using a tight-binding coherent potential approximation (CPA) model, we show that while the polarization of the net density of states is not correlated with the magnetic moment, the polarization of the density of states of {\it s} electrons is correlated with the magnetic moment in the same manner as observed by the tunneling experiments. We also discuss the spin polarization measurements by Andreev reflection experiments, some of which obtained different results from the tunneling experiments and our calculations.Comment: 8 RevTEX pages, 9 figures in ep

Diagnosis and Location of Pinhole Defects in Tunnel Junctions using only Electrical Measurements

In the development of the first generation of sensors and memory chips based on spin-dependent tunneling through a thin trilayer, it has become clear that pinhole defects can have a deleterious effect on magnetoresistance. However, current diagnostic protocols based on Andreev reflection and the temperature dependence of junction resistance may not be suitable for production quality control. We show that the current density in a tunnel junction in the cross-strip geometry becomes very inhomogeneous in the presence of a single pinhole, yielding a four-terminal resistance that depends on the location of the pinhole in the junction. Taking advantage of this position dependence, we propose a simple protocol of four four-terminal measurements. Solving an inverse problem, we can diagnose the presence of a pinhole and estimate its position and resistance.Comment: 9 pages, eplain TeX, other macro files included; some versions of TeX epsf may have trouble with figures, in which case try the Postscript or PDF generated automatically by the Archiv

Unit organization of four topics in American history

Thesis (M.A.)--Boston University, 1946. This item was digitized by the Internet Archive

Numerical analyses of the nonequilibrium electron transport through the Kondo impurity beside the Toulouse point

Nonequilibrium electron transport through the Kondo impurity is investigated numerically for the system with twenty conduction-electron levels. The electron current under finite voltage drop is calculated in terms of the `conductance viewed as transmission' picture proposed by Landauer. Here, we take into account the full transmission processes of both the many-body correlation and the hybridization amplitude up to infinite order. Our results demonstrate, for instance, how the exact solution of the differential conductance by Schiller and Hershfield obtained at the Toulouse point becomes deformed by more realistic interactions. The differential-conductance-peak height is suppressed below e^2/h with the width hardly changed through reducing the Kondo coupling from the Toulouse point, whereas it is kept unchanged by further increase of the coupling. We calculated the nonequilibrium local Green function as well. This clarifies the spectral property of the Kondo impurity driven far from equilibrium