Phys. Rev. B 76, 161403(R) (2007)
J. Barzola-Quiquia, P. Esquinazi, M. Rothermel, D. Spemann, T. Butz, and N. García
Abstract
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 Tc≳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.
