Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Internal magnetic field effect on magnetoelectricity in orthorhombic
  $RMnO_3$ crystals   We have investigated the role of the 4$f$ moment on the magnetoelectric (ME)
effect of orthorhombic $R$MnO$_{3}$ ($R$=rare earth ions). In order to clarify
the role of the 4$f$ moment, we prepared three samples: (Eu,Y)MnO$_{3}$ without
the 4$f$ moment, TbMnO$_{3}$ with the anisotropic 4$f$ moment, and
(Gd,Y)MnO$_{3}$ with the isotropic 4$f$ moment. The ferroelectric behaviors of
these samples are different from each other in a zero magnetic field.
(Eu,Y)MnO$_{3}$ and (Gd,Y)MnO$_{3}$ show the ferroelectric polarization along
the a axis in the ground state, while TbMnO$_{3}$ shows it along the c axis.
Such difference may arise from the influence of the anisotropic Tb$^{3+}$ 4$f$
moment. The direction of the ferroelectric polarization of $R$MnO$_{3}$ is
determined by the internal magnetic field arising from the 4$f$ moment.

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The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
26
The categories of this paper are: bayes-an
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The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
9
The categories of this paper are: nlin
36
The categories of this paper are: cmp-lg
8
The categories of this paper are: hep-ex
18
The categories of this paper are: econ
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The categories of this paper are: hep-th
13
The categories of this paper are: quant-ph