Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mean field theory and Monte Carlo simulation of Phase transitions and
  Magnetic Properties of a tridimensional Fe7S8 Compound   The structural, electronic and magnetic properties of Fe7S8 material have
been studied within the framework of the ab-initio calculations, the mean field
approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two
forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2
are the most probable configurations. A mixed Ising model with ferromagnetic
spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and
with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has
been used to study the magnetic properties of this compound. We demonstrated
that the magnetic phase transition can be either of the first or of the second
order, depending on the value of the exchange interaction and crystal field.
The presence of vacancies in every second iron layer leads to incomplete
cancellation of magnetic moments, hence to the emergence of the ferrimagnetism.
Anomalies in the magnetization behavior have been found and compared with the
experimental results.

27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
37
The categories of this paper are: supr-con
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
2
The categories of this paper are: math