Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vortex fluctuations and freezing of dipolar-coupled granular moments in
  thin ferromagnetic films   Below the Curie temperature T_c of a Heusler-alloy film, consisting of
densely packed, but exchange-decoupled nanograins, the spontaneous
magnetization M_s(T) and static in-plane susceptibility \chi_{||}(T) increase
very slowly signalizing a suppression of magnetization fluctuations. The
unpredicted variation \chi_{||}(T) ~ G_d^2(T), where G_d ~ M_s^2 is the
intergranular dipolar coupling, and also the magnetic freezing observed in the
dynamic susceptibility at lower temperatures is quantitatively reproduced by
Monte Carlo (MC) simulations with 10^4 dipolar-coupled moments on a disordered
triangular lattice. At high temperatures, the MC spin configurations clearly
reveal a dense gas of local vortex structures, which at low temperatures
condense in regions with stronger disorder. This vortex depletion upon
decreasing temperature seems to be responsible for the observed
\textit{increase} of the magnetic relaxation time. For weak disorder, the
temperature dependence of the MC vorticity and a singularity of the specific
heat at T_v=1/2 G_d(T_v)/k_B indicate a thermal transition from a vortex gas to
a state with a single vortex center plus linear vortex structures.

31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int