Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Structural, magnetic, and optical properties of zinc- and copper-
  substituted nickel ferrite nanocrystals
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
6
The categories of this paper are: astro-ph
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
15
The categories of this paper are: nucl-ex