Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the hyperfine interaction in rare-earth Van Vleck paramagnets at high
  magnetic fields   An influence of high magnetic fields on hyperfine interaction in the
rare-earth ions with non-magnetic ground state (Van Vleck ions) is
theoretically investigated for the case of $Tm^{3+}$ ion in axial symmetrical
crystal electric field (ethylsulphate crystal). It is shown that magnetic-field
induced distortions of $4f$-electron shell lead to essential changes in
hyperfine magnetic field at the nucleus. The proposed theoretical model is in
agreement with recent experimental data.

5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
34
The categories of this paper are: chem-ph
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio