STUDYING SPIN-DEPENDENT SCATTERING IN MAGNETIC MULTILAYERS BY MEANS OF PERPENDICULAR (CPP) MAGNETORESISTANCE MEASUREMENTS

Giant magnetoresistance (GMR) in multilayers composed of a ferromagnet ic (F) and a non-magnetic (N) metal is usually assumed to re suit prim arily from spin-orientation-dependent scattering in the bulk F metal a nd at the F-N interfaces, which are described by a bulk spin-asymmetry parameter beta and an interface parameter gamma. Measurements of the specific resistance, AR(t) the sample cross-sectional area A times res istance R(t), with the current perpendicular to the layer planes (CPP) , can give direct access to both parameters, as well as to the importa nt interface specific resistance, AR(F-N). We describe how these measu rements are performed at low temperatures, present the equations used to derive these parameters and discuss the conditions under which thes e 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 laye r thicknesses and the mean free paths for momentum transfer. We test t he equations against low temperature data on sputtered Co-Ag, Co-AgSn, Co-Cu and Py-Cu (Py=Ni84Fe16) multilayers, and list derived values of beta, gamma and AR(F-N) for Co-Ag, Co-Cu and Py-Cu. Asa further test, we examine how well the parameters found for the Co-Cu and Py-Cu mult ilayers predict the values of AR, for Co-Cu-Py-Cu multilayers in the s tates where neighboring Co and Py layer magnetizations are either para llel (P) or anti-parallel (AP) to each other. Lastly, Valet and Fert r ecently 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.