Atomic engineering of spin valves using Ag as a surfactant

In this study, dc magnetron sputtered NiO (50 nm)/Co (2.5 nm)/Cu(1.5 nm)/Co (3.0 nm) bottom spin valves were studied with and without Ag as a surfacta nt. At Cu spacer thickness of 1.5 nm, a strong positive coupling > 13.92 kA /m (> 175 Oe) between NiO-pinned and "free" Co layers leads to a negligible giant magnetoresistance (GMR) effect (<0.7%) in Ag-free samples. In contra st, spin valves deposited in the presence of approximate to1 monolayer of s urfactant Ag have sufficiently reduced coupling, 5.65 kA/m (71 Oe), which r esults in an order of magnitude increase in GMR (8.5%). Using transmission electron microscopy (TEM), the large positive coupling in Ag-free samples c ould directly be attributed to the presence of numerous pinholes. In situ x -ray photoelectron spectroscopy shows that, in Ag-containing samples, the l arge mobile Ag atoms float out to the surface during successive growth of C o and Cu layers. Detailed TEM studies show that surfactant Ag leaves behind smoother interfaces less prone to pinholes. The use of surfactants also il lustrates their efficacy in favorably altering the magnetic characteristics of GMR spin valves, and their potential use in other magnetoelectronics de vices and multilayer systems. (C) 2001 American Institute of Physics.