P-T Phase Diagram of LuFe2O4

Maria Poienar,Françoise Damay,Christine Martin,Maryvonne Hervieu,Thomas Hansen,Julien Haines,Jérôme Rouquette,Michael Hanfland,Gaston Garbarino,François Baudelet,Julie Bourgeois,Jean Bantignies,Patrick Hermet

doi:10.3390/cryst8050184

Abstract

The high-pressure behavior of LuFe2O4 is characterized based on synchrotron X-ray diffraction and neutron diffraction, resistivity measurements, X-ray absorption spectroscopy and infrared spectroscopy studies. The results obtained enabled us to propose a P-T phase diagram. In this study, the low pressure charge-ordering melting could be detected by synchrotron XRD in the P-T space. In addition to the ambient pressure monoclinic C2/m and rhombohedral R 3 ¯ m phases, the possible P 1 ¯ triclinic phase, the monoclinic high pressure form Pm and metastable modulated monoclinic phases were observed; the latter modulated monoclinic phases were not observed in the present neutron diffraction data. Furthermore, the transition to the Pm phase which was already characterized by strong kinetics is found to be favored at high temperature (373 K). Based on X-ray absorption spectroscopy data the Pm phase, which could be recovered at atmospheric pressure, can be explained by a change in the Fe-local environment from a five-fold coordination to a distorted 5 + 1 one.

Highlights

Magnetoelectric multiferroics combine ferroelectric and ferromagnetic properties in a single material, providing a possible route for controlling electric polarization with a magnetic field and magnetic order with an electric field [1]
XRDwe describe this new phase as a modulated monoclinic structure (MM)
We describe this new phase as a modulated monoclinic structure (MM)

Summary

Introduction

Magnetoelectric multiferroics combine ferroelectric and ferromagnetic properties in a single material, providing a possible route for controlling electric polarization with a magnetic field and magnetic order with an electric field [1]. LuFe2 O4 is considered as a prototype material in which ferroelectricity is driven by the electronic process of frustrated (Fe2+ /Fe3+ ) charge ordering (CO) which is coupled to magnetic order and magnetic fields [2]. The mixed valence compound LuFe2 O4 has been reported in the literature to crystallize at room temperature in the (R) R3m space group [6]. A monoclinic distortion (M1) was evidenced for the CO state, which disappears above TCO , and the crystal structure was refined in the monoclinic C2/m space group [7]. Along with the previously reported q2 and q3 modulations vectors distinctive of the charge-ordering (CO) of the iron species, an incommensurate order was observed characterized by a third vector q1 associated with a tiny oxygen deviation from the O4 stoichiometry [7]

Methods

Results

Conclusion