Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Contemporary Model Description of Magnetism   A treatment of many-electron polar and $s-d(f)$ exchange models is carried
out in connection with the development of the theory of magnetism of transition
and rare-earth metals, as well as their compounds. Particular emphasis is
placed on the derivation of the many-electron Heisenberg, Hubbard, Anderson and
$t-J$ models, as well as the internal relationship between them. Among the
topics discussed are many-electron approaches in describing systems of $d$- and
$f$-electrons, atomic representation of Hubbard's $X$-operators, slave-particle
representations, the problem of strong itinerant magnetism and the formation of
local moments, the role of non-quasiparticle (incoherent states). The
application of these concepts to strongly correlated systems, in particular, to
half-metallic ferromagnets and Kondo lattices, is discussed. A comparison is
performed with modern field-theoretical and topological approaches.

24
The categories of this paper are: dg-ga
21
The categories of this paper are: adap-org
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci