Spontaneous polarization and giant magnetoelectric effect at high magnetic fields in the borate system RT(BO) (R = rare earth, T=Fe, Al)

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18 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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Spontaneous polarization and g
iant magnetoelectric effect
at high magnetic fields in the borate
system
R
T
3
(BO
3
)
4

(R = rare earth, T=Fe, Al)

B. Lorenz
1
, K.
-
C. Liang
1
, Y. Y. Sun
1
, L. N. Bezmaternykh
2
, V. L. Temerov
2
, and C. W. Chu
1,3

1
TCSUH and Department of

Physics, University of Houston, Houston TX, 77204
-
5002, USA

2
Institute of Physics, Siberian Division, Russian Academy of Sciences, Krasnoyarsk, 660036,
Russia

3
Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA

Rare earth iro
n borates, RFe
3
(BO
3
)
4
,
belong to

a class of magnetoelectric materials which have
been studied lately because of their interesting magnetic properties, with mutually interacting Fe
spins and R
-
moments resulting in complex magnetic orders, and the strong cou
pling to the lattice
resulting in a significant magnetoelectric eff
ect. The compounds crystallize in the trigonal
huntite structure (space group R32, #155) and undergo a structural transition to P3
1
21 (#152).
Both space groups are non
-
centrosymmetric, but
also non
-
polar. The observed magnetoelectric
effect is therefore a result of a structural distortion in high magnetic fields. We discuss the
magnetic orders and the magnetoelectric effect as well as the spontaneous electric polarization
(only observed in H
oFe
3
(BO
3
)
4
) of several RFe
3
(BO
3
)
4
.

The isostructural compounds RAl
3
(BO
3
)
4

are of interest because
the d
-
electron spins of the Fe
are completely missing and the magnetic system is significantly simplified, including only f
-
moments of the rare earth ions. W
hile no magnetic long range order is observed, most members
of the compound family are magnetoelectric. A giant high
-
field magnetoelectric effect was
discovered in HoAl
3
(BO
3
)
4

with field
-
induced polarization values of up to 3600 μC/m
2

(at 70
kOe), exceedin
g field
-
induced values for linear or nonlinear magnetoelectrics and even
multiferroic compounds. The results are discussed together with the magnetic anisotropy of the
rare earth and the lattice strain induced by the external magnetic field.