Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: A magnetic phase-transition graphene transistor with tunable spin
  polarization
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
24
The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th