Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Equilibrium susceptibilities of superparamagnets: longitudinal &
  transverse, quantum & classical   The equilibrium susceptibility of uniaxial paramagnets is studied in a
unified framework which permits to connect traditional results of the theory of
quantum paramagnets, $\Sm=1/2, 1, 3/2$, ..., with molecular magnetic clusters,
$\Sm\sim5, 10, 20$, all the way up, $\Sm=30, 50, 100$,... to the theory of
classical superparamagnets. This is done using standard tools of quantum
statistical mechanics and linear response theory (the Kubo correlator
formalism). Several features of the temperature dependence of the
susceptibility curves (crossovers, peaks, deviations from Curie law) are
studied and their scalings with $\Sm$ identified and characterized. Both the
longitudinal and transverse susceptibilities are discussed, as well as the
response of the ensemble with anisotropy axes oriented at random. For the
latter case a simple approximate formula is derived too, and its range of
validity assessed, so it could be used in modelization of experiments.

16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
1
The categories of this paper are: cs
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
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess