Modification of the magnetic properties of polyimide films by cobalt ion implantation

The magnetic characteristics of polyimide films implanted with Co$^+$ ions with an energy of 40 keV in the dose range $D$ = 2.5 $\cdot$ 10$^{16}$–1.25 $\times$ 10$^{17}$ cm$^{-2}$ at ion current densities $j$ = 4, 8, and 12 $\mu$A/cm$^2$ have been investigated. It has been shown that, at implantation doses of less than 5 $\times$ 10$^{16}$ cm$^{-2}$, the superparamagnetic properties of modified samples are described by the Langevin equation. At higher doses, there is an intercluster interaction. It has been found that, with an increase in the ion current, the cluster size decreases. The sizes of the formed clusters are determined and vary in the range from 3.9 to 11.0 nm, depending on the implantation dose.