Annealed Cobalt–Carbon Nanocomposites for Room-Temperature Spintronic Applications

We report on direct writing of functional nanostructures of Co–C–O nanocomposites by use of the focused-electron-beam-induced deposition (FEBID) with the organometallic precursor Co₂(CO)₈. The magneto-transport properties and the quasi-static magnetization process of Co–C–O deposits were tuned upon ex-situ postannealing from room-temperature up to 300 °C under high-vacuum. The magnetic coercivity increasing by about 1 order of magnitude upon annealing is attributed to the domain wall pinning in the magnetization reversal process. In addition, the anisotropic magnetoresistance (AMR) of the annealed deposits reached around 1.8%, being among the highest values reported for FEBID materials. It is in the range of 20–110% larger than the AMR of pure Co thin films and nanowires, while about 176% larger compared to Co–C deposits grown by FEBID with higher metal content. The magnetotransport measurements reveal that the AMR is enhanced by the domain-wall magnetoresistance (DWMR) effect in the annealed deposits. The incorporation of graphitic carbon in ferromagnetic deposits is a key for significant improvements in the coercivity and the reversal fields, as well as the observed huge AMR values. It yields this material especially advantageous for potential applications in magnetic memory, high density magnetic recording, and room-temperature spintronic technology.