Experimental evidence for two-dimensional magnetic order in proton bombarded graphite

We have bombarded graphite samples with protons at low temperatures and low fluences to attenuate the large thermal annealing produced during irradiation. The overall optimization of sample handling allowed us to find Curie temperatures T-c greater than or similar to 350 K at the fluences used. The magnetization versus temperature shows unequivocally a linear dependence, which can be interpreted as due to excitations of spin waves in a two-dimensional Heisenberg model with a weak uniaxial anisotropy.