Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Magnetic-Field and External-Pressure Control of Ferroelectricity in
  Multiferroic Manganites   We have investigated dielectric properties in a series of crystals of
$R$MnO$_{3}$ ($R$ is a rare earth ion) under magnetic fields and
quasihydrostatic pressure. We have found that ferroelectric phase appeared in
GdMnO$_3$ crystal below 13K. We have confirmed that a small spontaneous
polarization exists along a axis ($P_a$) in the orthorhombic $Pbnm$ setting and
that $P_a$ can be reversed by the dc electric field. The dielectric anomaly due
to the ferroelectric transition accompanied thermal hysteresis and lattice
striction. The ferroelectric transition temperature decreased with
quasihydrostatic pressure. These results indicate that the ferroelectric
transition is improper and is of the first-order displacement-type one. $P_a$
was easily collapsed by application of magnetic field of 0.4T parallel to the
spin-canting direction ($H \| c$) while it was enhanced parallel to the easy
axis ($H \| b$).

25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
27
The categories of this paper are: comp-gas
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph
11
The categories of this paper are: hep-lat