Gallium Iron room temperature Magnetoelectric Oxides
Zusammenfassung der Projektergebnisse
This is a French-German collaborative project, involving three teams at three locations. The aim of the project was an investigation of the possibilities offered by gallium ferrite, Ga2-xFexO3 (GFO), in terms of multiferroicity and magnetoelectricity. When the project was initiated, the material was known in its bulk form, mainly in single crystals. It was known since the 60s to be ferrimagnetic, with a non-zero magnetization in zero-field and a Néel temperature increasing with x, above room temperature for x>1.2. It was known to crystallize in a space group which allows ferroelectricity, but its ferroelectric behavior had never been demonstrated. Its magnetoelectric behavior had been evidenced in single crystals, but its mechanism was not completely clear. Some thin films had been produced by one team, but not with a high epitaxial crystalline quality. The challenges we decided to tackle were threefold: production of high crystalline quality GFO compounds, pure and doped, in the polycrystalline bulk form but also, and more importantly, in the form of epitaxial thin films, needed for potential applications; characterization of the electric and magneto-electric properties of the materials, with a particular stress on the thin films, for which numerous artefacts are known to be possible; extended theoretical study of the material, in order to both understand the observations and predict the best suited composition for optimal ferroelectric polarization and magnetoelectric coupling. The scientific approach was to first optimize the elaboration techniques for the production of the material, using the ceramics method for bulk and pulsed laser deposition for epitaxial thin films. After basic structural, compositional, and magnetic characterization, the ferroelectric and magnetoelectric properties of the samples were thoroughly studied through I-V curves, PUND measurements, piezo force microscopy, low-energy electron microscopy, photoemission electron microscopy and transmission electron microscopy. While the experimental part of the study was conducted by the French partners, on the German side the theoretical aspects of the ferroelectric and magnetoelectric properties of the compound were addressed in parallel using ab initio theoretical tools. The results of this study were used as an input to the choice of the elaboration part of the project. Major results of the project have been the demonstration of the ferroelectricity and magnetoelectricity of GFO in thin films, as well as a theoretical model which describes a novel ferroelctric switching mechanism of both GFO and structurally related ε-phase of Fe2O3 (eFO). The ferroelectric switching necessitated the reduction of leakage currents through doping. Since for high Fe contents GFO thin films are ferrimagnetic with a Néel temperature above room temperature and non-zero room temperature magnetization, we have demonstrated that GFO thin films are room temperature multiferroics. Dr. Konstantin Rushchanskii was employed in the German group participating in the GALIMEO project and was financed by the DFG. We applied ab-initio methods in order to understand the properties of the stoichiometric and offstoichiometric GFO, magnetoelectric coupling, site preferences of possible dopants and the switching mechanism of the ferroelectric polarisation.
Projektbezogene Publikationen (Auswahl)
- “Ab initio study of magneto-phonon interaction in GaFeO3” Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Regensburg, Germany, 10 Mar 2013 - 15 Mar 2013
Rushchanskii, K. ; Blügel, S. ; Ležaić, M.
- ”Structural parameters, magnetophonon interaction and magnetoelectric effect in GaFeO3: an ab initio study”, Workshop ”Challenges in Multiferroics/Magnetoelectrics”, Strasbourg, France, 04-06 Dec. 2013
Rushchanskii, K.; Blügel, S.; Ležaić, M.
- “Ab initio characterization of magnetoelectric effect in GaFeO3”. JSPS Core-to-Core Program, Advanced Research Networks: International Workshop of Computational Nano-Materials Design on Green Energy, Osaka, Japan, 1 Jun 2014 - 3 Jun 2014
Rushchanskii, K.; Blügel, S.; Ležaić, M.
- “Multiferroicity in GaFeO3: ab initio understanding of structure and magnetoelectric interaction in pristine and offstoichiometric crystals” Challenges in Multiferroics & Magnetoelectrics, Forschungszentrum Jülich, Germany, 12 Oct 2015 - 14 Oct 2015
Rushchanskii, K.; Blügel, S.; Ležaić, M.
- “Ferroelectric switching in multiferroic Ga0.5Fe1.5O3 and ε-Fe2O3”. EU-JAPAN Workshop on Computational Materials Design and Realization for Spintronics, Moltronics, Quantronics, Superconductivity and Topotronics, Forschungszentrum Jülich, Germany, 18 Sep 2016 - 30 Sep 2016
Rushchanskii, K.; Blügel, S.; Ležaić,M.
- “Multiferroicity in off-stoichiometric GaxFe1−xO3”. Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Regensburg, Germany, 6 Mar 2016 - 11 Mar 2016
Rushchanskii, K.; Blügel, S.; Ležaić, M.
