S.-F. Lee

Two-channel analysis of CPP-MR data for Ag/Co and AgSn/Co multilayers

Abstract We present a 2-channel model for the magnetoresistance of a magnetic multilayer with the current flowing perpendicular to the layer planes (CPP-MR), and show that the model fits previous data on Ag/Co and new data on AgSn/Co multilayers better than our previous simple series resistance model. The 2-channel model supports the conclusions previously reached for Ag/Co, and permits a determination of the spin-orientation-dependent parameters α Co = 2.9(+0.5, -0.3) and α Ag / Co = 12(+5, -2).

Giant magnetoresistance with current perpendicular to the multilayer planes

Abstract We review recent progress in measuring giant magnetoresistance in magnetic multilayers with the current flowing perpendicular to the multilayer planes (CPP-MR), and present new data for Co/Cu and Co/Ag multilayers.

Giant magnetoresistance with current perpendicular to the layer planes of Ag/Co and AgSn/Co multilayers (invited)

A two‐channel model of electronic conduction is shown to provide a satisfactory description of the magnetoresistances of Ag/Co and AgSn/Co multilayers with the current flowing perpendicular to the layer planes. A combination of data for as‐prepared samples at magnetic field H=0 (for which the magnetization M≊0), and for the same samples in the ferromagnetically ordered state, is used to extract ‘‘best’’ spin‐orientation‐dependent parameters of αCo=2.9(+0.5,−0.3) and αCo/Ag=12(+5,−2) from Ag/Co data and αCo=2.4(+1,−0.7) and αCo/AgSn=11(+7,−4) from AgSn/Co data.

Magnetic states of magnetic multilayers at different fields

The resistance of an as‐sputtered magnetic multilayer in zero applied magnetic field can be considerably different from the maximum resistance measured after the multilayer has been cycled to above its saturation field. We examine the relation between these two resistances in some Ag/Co, Cu/Co, and Cu/NiFe multilayers, and its implications for interpreting giant magnetoresistance.

Studying spin-dependent scattering in magnetic multilayers by means of perpendicular (CPP) magnetoresistance measurements

Abstract Giant magnetoresistance (GMR) in multilayers composed of a ferromagnetic (F) and a non-magnetic (N) metal is usually assumed to result primarily from spin-orientation-dependent scattering in the bulk F metal and at the FN interfaces, which are described by a bulk spin-asymmetry parameter β and an interface parameter γ. Measurements of the specific resistance, AR t the sample cross-sectional area A times resistance R t , with the current perpendicular to the layer planes (CPP), can give direct access to both parameters, as well as to the important interface specific resistance, AR FN . We describe how these measurements are performed at low temperatures, present the equations used to derive these parameters and discuss the conditions under which these equations are valid—the most important being that the spin diffusion lengths l sf in the N and F metals must be much longer than the layer thicknesses and the mean free paths for momentum transfer. We test the equations against low temperature data on sputtered CoAg, CoAgSn, CoCu and PyCu (PyNi 84 Fe 16 ) multilayers, and list derived values of β, γ and AR FN for CoAg, CoCu and PyCu. As a further test, we examine how well the parameters found for the CoCu and PyCu multilayers predict the values of AR t for CoCuPyCu multilayers in the states where neighboring Co and Py layer magnetizations are either parallel (P) or anti-parallel (AP) to each other. Lastly, Valet and Fert recently generalized these equations to shorter values of l sf , and we show how their results can be used to derive l sf for AgMn and AgPt alloys.

How to isolate effects of spin‐flip scattering on giant magnetoresistance in magnetic multilayers (invited)

A technique is described for isolating effects of finite spin diffusion lengths on the magnetoresistance (MR) of magnetic multilayers at low temperatures by measuring the MR with the current perpendicular to the layer planes. Applying this technique to relatively concentrated Co/AgMn and Co/CuMn multilayers yields large effects, generally consistent with expectations from a theory by Valet and Fert [Phys. Rev. B 48, 7099 (1993)]. However, some complicating issues still need to be resolved.

Giant CPP-magnetoresistance of Ni/Ag multilayers

Abstract The first measurements are presented of the Giant Magnetoresistance (MR) of Ni/Ag multilayers with Current Flow Perpendicular to the layer planes (CPP-MR). As previously seen in Co/Ag and Co/Cu multilayers, at 4.2K the CPP-MR is typically much larger than the more usual Giant MR with Current flow In the layer Planes (CIP-MR). Both the CPP-MR and the CIP-MR for Ni/Ag are smaller than those for equivalent Co/Ag and Co/Cu multilayers.

Perpendicular resistance of thin Co films in contact with superconducting Nb

Abstract Perpendicular resistance measurements are reported for sputtered Nb/Co/Nb sandwiches where the thickness of the Co was varied from 6nm to 1200nm. These measurements yield a boundary resistance Between the ferromagnetic Co and the superconducting NB of (3.2 ± 0.2) fωm 2 .