Highly deleterious role of small amounts of carbon on the giant magnetoresistance effect

Abstract

Carbon (in the form of hydrocarbons) is a common contaminant in high and ultra-high-vacuum systems, and easily gets incorporated in films during deposition. This work reports the highly deleterious role of small amounts of carbon on the structure and magnetic properties of “giant” magnetoresistance (GMR) spin valves. Controlled incorporation of 1–3 at. % carbon in Co/Cu layers of NiO–Co–Cu-based spin valves has been found to completely eliminate the GMR effect. Transmission electron microscopy (TEM) shows that carbon promotes highly discontinuous Co/Cu layers, resulting in a large number of pinholes; domain studies corroborate that the “free” layer under the influence of a large pinhole coupling is unable to switch independently of the “pinned” Co layer. These results also have implications for other multilayers and spintronics devices.

Magnetism in ultrathin film structures

“…As an illustration, recent growth studies have led to an improved understanding of the role of surfactants in controlling interface structure at the atomic scale. Such effects can be used to dramatically influence magnetic properties in ultrathin films by controlling the interface roughness-for example, the surfactant effect of minute amounts of oxygen in the 10 −9 mbar range can significantly affect the magnitude of the giant magnetoresistance in spin-valve structures [134], while 1-3 at% carbon in Co/Cu spin-valves can eliminate the GMR effect altogether [135,136]. Submonolayer coverages of non-magnetic materials can change the magnetic anisotropy of ultrathin films, in some cases causing a complete reorientation of the magnetic easy axis [137][138][139][140].…”