Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Interacting electron spins in $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]I
  investigated by ESR spectroscopy   We performed angular and temperature-dependent electron-spin-resonance
measurements in the quasi-two-dimensional organic conductor
$\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]I. The interlayer spin-diffusion is much
weaker compared to the Cl- and Br-analogues, which are antiferromagnetic
insulator and paramagnetic metal, respectively;
$\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]I behaves insulating when cooled below $T$
= 200 K. A spin gap ($\Delta\approx$ 18 K) opens at low temperatures leading to
a spin-singlet state. Due to intrinsic disorder a substantial number of spins
($\sim$ 1 $\%$) remains unpaired. We observe additional signals below $T$ = 4 K
with a pronounced anisotropy indicating the presence of local magnetic moments
coupled to some fraction of those unpaired spins.

20
The categories of this paper are: acc-phys
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom