Interdiffusion in CoFe/Cu multilayers and its application to spin-valve structures for data storage

Abstract

Spin-valve structures might be exposed to higher temperatures in future disk drive applications and might thus degrade faster than it does today if proper materials and methods are not used. In order to determine whether this degradation is due to interdiffusion between constituent layers or is dominated by other phenomena, the interdiffusion coefficients for all layers in the spin valve have to be determined. For diffusion driven degradation it would then be possible to predict lifetimes based on a maximum allowed reduction in ΔR/R where R is the resistivity. Here we report the initial results for a CoFe/Cu interface, common to many spin-valve structures. Interdiffusion in (111) textured polycrystalline CoFe/Cu multilayers has been measured and quantified by x-ray reflectometry. Bulk diffusion is dominant at temperatures above ∼540 °C and is described by an activation energy of Ea=2.41 eV and a prefactor of D0=2.92×10−8 m2/s. Below temperature of 540 °C grain boundary diffusion dominates and is characterized by Ea=0.90 eV and D0=1.91×10−17 m2/s. Prior to stabilization of the diffusion process there is an initial rapid change in the (111) texture. During initial “sharpening” of the CoFe/Cu multilayer interfaces there is shortening of the periodicity as well as a decrease in out-of-plane lattice spacing.