Improved interfaces and magnetic properties in spin valves using Ni80Fe20 seed layer

Abstract

The “giant” magnetoresistance (GMR) (Ni80Fe20)O–Co–Cu based “top” spin valves were studied with and without Ni80Fe20 as a seed layer. Microstructure examination shows that without the seed layer, the “free” and the “pinned” Co layers of the spin valves are highly irregular, discontinuous, and connected by pinholes across the Cu spacer layer, resulting in a large coupling >5.96 kA/m (>75 Oe) and a negligible GMR effect (<0.7%). The presence of Ni80Fe20 seed layer leads to continuous layers without pinholes and smooth interfaces in the (Ni80Fe20)O–Co–Cu, thereby essentially eliminating the coupling between the “free” and the “pinned” layers (0.23 kA/m or 2.9 Oe), a more than 25-fold reduction with respect to the seedless spin valves. Reduced detrimental coupling results in more than an order of magnitude increase in GMR (8.5%) in the NiFe seed layer spin valves. Domain studies confirm that the “pinned” and the “free” layers in seedless spin valves reverse their magnetization in an overlapping field range, and independently in spin valves deposited in the presence of a seed layer.

[Ni80Fe20/Cu/Co/Cu] spin-valve multilayers electrodeposited on NiFe buffer layers

“…It has been widely reported that the microstructures, especially the textures and roughness of films may affect the magnetic properties significantly [8][9][10], so spin-valve systems are usually grown on thin buffer layers such as Ta, NiFe, Fe, Cu, etc. [11,12]. In addition, the nucleation of deposit on semiconductor usually requires an extra cathodic overpotential [13], which may induce the fluctuation of current flow.…”