MULTIFERROICS
Room temperature magnetoelectric coupling in a
molecular ferroelectric ytterbium(III) complex
Jérôme Long^1 *, Maxim S. Ivanov^2 , Vladimir A. Khomchenko^2 , Ekaterina Mamontova^1 ,
Jean-Marc Thibaud^1 , Jérôme Rouquette^1 , Mickaël Beaudhuin^1 , Dominique Granier^1 ,
Rute A. S. Ferreira^3 , Luis D. Carlos^3 , Bruno Donnadieu^4 , Marta S. C. Henriques^2 ,
José António Paixão^2 , Yannick Guari^1 , Joulia Larionova^1
Magnetoelectric (ME) materials combine magnetic and electric polarizabilities in the same phase,
offering a basis for developing high-density data storage and spintronic or low-consumption devices
owing to the possibility of triggering one property with the other. Such applications require strong
interaction between the constitutive properties, a criterion that is rarely met in classical inorganic ME
materials at room temperature. We provide evidence of a strong ME coupling in a paramagnetic
ferroelectric lanthanide coordination complex with magnetostrictive phenomenon. The properties of this
molecular material suggest that it may be competitive with inorganic magnetoelectrics.
A
ferroelectric material exhibits a perma-
nent electrical polarization that can be
switched by an electric field ( 1 , 2 ). Such
electroactive materials have a wide range
of applications, including temperature
sensing, data storage, piezoelectric devices, and
electro-optics. The association of electrical and
magnetic polarizabilities gives rise to multi-
functional systems called magnetoelectrics.
The term describes the influence of a magnetic
(electric) field on the polarization (magnetization),
allowing the constitutive properties to be simul-
taneously triggered ( 3 , 4 ). For computing, modify-
ing the polarization or magnetization using a
low-magnitude magnetic or electric field may
reduce the energy needed and speed up the
processing rate of nonvolatile memory devices
( 3 , 5 , 6 ). Conventional approaches to designing
single-phase magnetoelectrics are widely based
on inorganic materials, such as oxides or fluorides
( 6 – 8 ). However, if the origins of ferroelectricity
and magnetism are associated with different
carriers, we should expect only a moderate mag-
netoelectric (ME) coupling ( 9 ). For instance,
only a few examples exist of ME coupling at
room temperature ( 6 , 10 , 11 ). In contrast, large
ME coupling has been found in strain-mediated
multiphase materials, such as composites or
multilayers, by combining piezoelectricity with
themagnetostrictiveeffect( 3 ).
Molecular materials exhibit numerous ad-
vantages over inorganic ones, such as structural
diversity, soft chemistry routes, environmen-
tally friendly processing and shaping, optical
transparency, and light density ( 12 ). For these
reasons, molecular ferroelectrics ( 13 , 14 ) are
often considered an alternative to traditional
metal oxides ( 15 , 16 ). Although most molecular
materials exhibit a magnetic ordering temper-
ature below room temperature, important ME
coupling may be expected from the association
of paramagnetism and ferroelectricity (fig. S1)
( 7 ), as both these properties could involve the
same chemical element. Although ME coupling
in nonferroelectric molecular materials has
been reported ( 17 , 18 ), the interaction between
magnetism and ferroelectricity has not been
extensively studied ( 19 – 26 ). For the few examples
that exist, the ferroelectric ordering tempera-
tures are typically lower than room temperature.Moreover, the modification of the polarization
or magnetization by applying magnetic or
electric fields, respectively—which also remains
challenging in pure inorganic materials—
requires a large magnitude operating field ( 27 ).
We designed a chiral lanthanide complex
exhibiting an above–room temperature ferro-
electricity that, in association with a strong
magnetostriction, gives rise to a distinctive ME
coupling. This allowed tuning of the ferroelectric
domains at the nanometric scale by applying
a relatively low magnetic field at room temper-
ature. Our molecular approach to designing
ME materials relied on the association of para-
magnetic lanthanide ions, such as Yb3+, with
a chiral diamagnetic zinc complex in order
to favor the crystallization in 1 of the 10 polar
point groups compatible with ferroelectricity.
We chose the Yb3+ion because it has a large
total magnetic moment, which, being oriented
along a magnetic field, can provide an aniso-
tropic magnetostriction underlying the coupling
between magnetic and structural subsystems.
The stoichiometric reaction ofR,R-H 2 L
[6,6'-((1E,1'E)-(((1R,2R)-1,2-diphenylethane-
1,2-diyl)bis(azaneylylidene))bis(methane-
ylylidene))bis(2-methoxyphenol)] orS,S-H 2 L
[6,6'-((1E,1'E)-(((1S,2S)-1,2-diphenylethane-1,2-
diyl)bis(azaneylylidene))bis(methaneylylidene))
bis(2-methoxyphenol)], Zn(OAc) 2 ·2H 2 O, and
Yb(NO 3 ) 3 ·5H 2 O in methanol yielded to a yel-
low solution, which, upon slow diffusion of
diethylether, resulted in the crystallization
ofR,R-[Zn(OAc)(L)Yb(NO 3 ) 2 ](R,R-1)orS,S-
[Zn(OAc)(L)Yb(NO 3 ) 2 ](S,S-2). Using singleRESEARCH
Longet al.,Science 367 , 671–676 (2020) 7 February 2020 1of5
(^1) Institut Charles Gerhardt Montpellier, UMR 5253, Université
de Montpellier, ENSCM, CNRS, Place E. Bataillon, 34095
Montpellier Cedex 5, France.^2 CFisUC, Department of Physics,
University of Coimbra, 3004-516 Coimbra, Portugal.^3 Physics
Department and CICECO–Aveiro Institute of Materials,
University of Aveiro, 3810-193 Aveiro, Portugal.^4 Fédération de
Recherche Chimie Balard–FR3105, Université de Montpellier,
Place E. Bataillon, 34095 Montpellier Cedex 5, France.
*Corresponding author. Email: [email protected]
Fig. 1. Crystal structures ofR,R-1 andS,S-2.(A) Molecular structure of the dinuclear Zn2+-Yb3+complexes
R,R- 1 andS,S- 2 and their enantiomeric relationship. Orange, Yb3+; light blue, Zn2+; blue, N; red, O; gray,
C. Hydrogen atoms have been omitted for clarity. (B) View of the crystal packing arrangement ofR,R- 1 along
theaaxis, emphasizing the two homochiral complexes. (C) Single-crystal facets assignment and view
of the slice in the crystallographicð 0 1 1 Þplane.