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Irradiation Enhanced paramagnetism on graphene nanoflakes

We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 10^11- 10^17 ions/cm2. The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 10^15 /cm^2. However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and X-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5K