Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental Evidence for Two-Dimensional Magnetic Order in Proton
  Bombarded Graphite   We have prepared magnetic graphite samples bombarded by protons at low
temperatures and low fluences to attenuate the large thermal annealing produced
during irradiation. An overall optimization of sample handling allowed us to
find Curie temperatures $ T_c \gtrsim 350$ K at the used fluences. 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.

17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph