Test of unified picture of spin-dependent transport in perpendicular (CPP)giant magnetoresistance and bulk alloys

Measurements of current perpendicular (CPP) magnetoresistance (MR) on hybri d and exchange-biased spin valves allow determination of the layer anisotro py parameter beta for ferromagnetic alloys, thus allowing testing of whethe r this CPP beta is similar to values obtained from direct measurements on, and theoretical estimates for, dilute bulk ferromagnetic alloys. Of special interest are alloys where beta is expected to be negative. In this article , we derive a value of beta for a Ni97Cr3 alloy using such spin valves base d upon permalloy. We confirm prior CPP-MR results that this beta is negativ e, but our inferred value, beta=-0.35+/-0.1, is closer to bulk and theoreti cal estimates. Our data thus provide new support for a unified picture of b eta in the CPP-MR and bulk alloys. We also derive a short spin-diffusion le ngth in NiCr, l(sf)=3+/-1 nm. (C) 1999 American Institute of Physics. [S002 1-8979(99)19108-4].