Abstract
NiMn/NiFe/Co/Cu/Co/NiFe/seed layer and NiFe/CoFe/Cu/CoFe/Ru/CoFe/NiFe/NiMn/seed layer structures have been investigated using high resolution transmission electron microscopy (HRTEM) coupled with nanobeam energy dispersive X-ray (EDX) and electron energy loss spectroscopy (EELS). An accumulated sum technique was applied to analyse the lattice spacing variation across the ultra-thin film from HRTEM micrographs. A Wiener filter was used to remove the electron beam broadening effect from nanobeam EDX data to improve the spatial resolution of composition profiles. A combination of these two techniques (lattice variation measurement and the deconvolution of nanobeam EDX) allows any interdiffusion effects between the ultra-thin films in the spin-valve devices to be revealed. The compositional analysis shows that diffusion of Mn and Ni into the Cu/Co bilayer is only observed in the Co/Cu/Co sample. This result indicates that the Ru layer in the CoFe/Cu/CoFe sample might not only act as a spacer of the synthetic antiferromagnet but also behaves as a good diffusion barrier for Ni and Mn elements in the spin valve structure. The diffusion coefficients of constituent elements are simply determined by using the Matano-Boltzmann method from the deconvoluted compositional profiles. Diffusion of Cu in Co and Ni in Co is primarily by the grain boundary mechanism. In the CoFe/Cu/CoFe/Ru/CoFe sample, diffusivity of Cu and Ni is smaller than that in the Co/Cu/Co sample. © 2003 Elsevier Science B.V. All rights reserved.