Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Direct coupling of ferromagnetic moment and ferroelectric polarization
  in BiFeO$_3$   The spin-driven component of electric polarization in a single crystal of
multiferroic BiFeO$_{3}$ was experimentally investigated in pulsed high
magnetic fields up to 41 T. Sequential measurements of electric polarization
for various magnetic field directions provide clear evidence of electric
polarization normal to the hexagonal $c$ axis (${\bf P}_{\rm t}$) in not only
the cycloidal phase, but also the field-induced canted antiferromagnetic phase.
The direction of ${\bf P}_{\rm t}$ is directly coupled with the ferromagnetic
moment in the canted antiferromagnetic phase, and thus controlled by changing
the direction of the applied magnetic field. This magnetoelectric coupling is
reasonably reproduced by the metal-ligand hybridization model.

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The categories of this paper are: q-bio
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
20
The categories of this paper are: acc-phys
27
The categories of this paper are: comp-gas
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
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The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph