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

Abstract

Measurements of current perpendicular (CPP) magnetoresistance (MR) on hybrid and exchange-biased spin valves allow determination of the layer anisotropy parameter β for ferromagnetic alloys, thus allowing testing of whether this CPP β is similar to values obtained from direct measurements on, and theoretical estimates for, dilute bulk ferromagnetic alloys. Of special interest are alloys where β is expected to be negative. In this article, we derive a value of β for a Ni97Cr3 alloy using such spin valves based upon permalloy. We confirm prior CPP-MR results that this β is negative, but our inferred value, β=−0.35±0.1, is closer to bulk and theoretical estimates. Our data thus provide new support for a unified picture of β in the CPP-MR and bulk alloys. We also derive a short spin-diffusion length in NiCr, lsf=3±1 nm.