Irradiation-Induced Magnetism in Carbon Nanostructures

Nitrogen (${}^{15}\mathrm{N}$) and carbon (${}^{12}\mathrm{C}$) ion implantations with implant energy of 100 keV for different doses were performed on nanosized diamond (ND) particles. Magnetic measurements on the doped ND show ferromagnetic hysteresis behavior at room temperature. The saturation magnetization ($M_{\mathrm{s}}$) in the case of ${}^{15}\mathrm{N}$ implanted samples was found to be higher compared to the ${}^{12}\mathrm{C}$ implanted samples for dose sizes greater than ${10}^{14}{\mathrm{cm}}^{-2}$. The role of structural modification or defects along with the carbon-nitrogen (C-N) bonding states for the observed enhanced ferromagnetic ordering in ${}^{15}\mathrm{N}$ doped samples is explained on the basis of x-ray photoelectron spectroscopy measurements.

Figure 1

(a) Magnetization as a function of the applied field for the sample with dose size $5\times {10}^{14}/{\mathrm{cm}}^2$ from the first set of implants. (b) Ferromagnetic signals from the ${}^{15}\mathrm{N}$ implanted nanodiamonds for various doses from the second batch of samples presented.

Figure 2

Top: Saturation magnetic moment (open circles: first set of experiments; solid squares: second set of experiments) as a function of dose size for ${}^{15}\mathrm{N}$ implants. Bottom: Comparison of the experimental values of saturation magnetic moments for ${}^{15}\mathrm{N}$ (solid squares) and ${}^{12}\mathrm{C}$ (solid circles) implants.

Figure 3

XPS of the nanodiamond samples. (a)–(d) XPS spectra for carbon core level peaks. (a) Pristine nanodiamond. (b) Ion implanted ND with dose sizes $5\times {10}^{14}/{\mathrm{cm}}^2$, (c) $1\times {10}^{15}/{\mathrm{cm}}^2$, and (d) $1\times {10}^{17}/{\mathrm{cm}}^2$. (e)–(h) XPS spectra showing nitrogen core level peaks. (e) Pristine nanodiamond. (f) Ion implanted ND with dose sizes $5\times {10}^{14}/{\mathrm{cm}}^2$, (g) $1\times {10}^{15}/{\mathrm{cm}}^2$, and (h) $1\times {10}^{17}/{\mathrm{cm}}^2$.