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Relations Structure-Propriétés et transitions structurales dans les ferroélectriques électroniques LuFe2O4 en fonction de la Pression et de la Température – RESPECT

Submission summary

Materials that are simultaneously ferroelectric and ferromagnetic are gaining more and more interest. Such a coupling between ferroelectric and ferromagnetic properties could lead to electric-field switchable magnetization or vice versa. This coupling would lead to totally new possibilities in the design of data storage devices. Unfortunately, the mechanism driving the conventional ferroelectricity such (PbTiO3) is incompatible with the existence of a spontaneous magnetic moment. The off-centering of the Ti-ion in PbTiO3 is stabilized by lowering energy of covalent bond formation, in which charge transfers from the filled oxygen 2p orbitals into the d states of the transition metal ion, which must be empty for this mechanism to be favorable. On the other hand, a partly filled d shell is necessary for magnetism to occur in metal ions which will break the strong covalent bond necessary for ferroelectricity. This is why very few magnetoelectric multiferroics exist. A possible way to avoid this incompatibility was reported by Efremov et al. based on charge-ordered and orbitally-ordered manganites perovskites . From the point of view of ferroelectricity, this kind of charge configuration has notable similarity with the coherent arrangement of electric dipoles discussed commonly in conventional ferroelectric materials (PbTiO3). Unfortunately, these proposed charge-ordered multiferroics in manganites perovskites are unlikely to be of immediate practical use in terms of device applications. The electric polarization is very small and the magnetic ordering is essentially antiferromagnetic. Additionally, the electric and magnetic ordering temperatures are still far below room temperature. Recently, a new origin of ferroelectricity was found in LuFe2O4 based on the specific configuration of charge ordering. In this material, the polar ordering arises from the repulsive property of electron-electron correlations acting on a frustrated geometry. Additionally, giant room temperature magnetodielectric response has also been reported, giving rise to a new generation of multifunctional devices for microelectronics. LuFe2O4 has a hexagonal layered structure (space group R3 ̅m, a = 3.44 Å and c = 25.28 Å). Below 330 K a charge frustration occurs based on the detection of a corresponding superstructure reflection, which indicates a transformation to a three dimensional charge ordering. The goal of this work will be to use the effect of pressure to gain a deep insight into the origin of electronic ferroelectricity in LuFe2O4. The experimental project requires the use of several characterization methods in order to improve our fundamental understanding of the different electrical, structural and electronic process taking place at the nano-, micro- and macro-scopic levels: 1) X-ray and neutron diffraction, 2) EXAFS, 3) Mössbauer spectroscopy and 4) dielectric and piezoelectric measurements. Owing to the complexity of these materials, the use of different techniques is essential for their characterization. Hence, the strength of our project is also related to the complementarities of the three young researchers from the synthesis of the materials, Denis Balitskiy, to the high-pressure characterization, Jérôme Rouquette and to the set-up of a unique experiment of P-T Mössbauer spectroscopy in France, Laurent Aldon. This collaboration should bring new insight in the understanding of this new kind of ferroelectric materials. In conventional ferroelectricity, pressure is found to reduce, and even annihilate for high enough value the electric polarization. As the origin of ferroelectricity in LuFe2O4 is based on electron repulsion, pressure is expected to enhance the polar order. Therefore, the pressure variable appears as the appropriate parameter to investigate LuFe2O4 family of materials in the attempt to increase the TC of this ferroelectric material; one can expect a positive slope of the ferroelectric-paraelectric transition in the P-T space. This knowledge is essential for the optimization of the physical properties of this material, and on the longer term, for the development of new ferroelectric-based materials.

Project coordination

Jérôme ROUQUETTE (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.


Help of the ANR 159,604 euros
Beginning and duration of the scientific project: - 36 Months

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