Magnetic materials are heavily used in the dynamic storage of information (hard disk drive, head for reading). For these applications, they are most often designed in the form of thin films. This was achieved after the birth of the spin electronics or "spintronics" and the discovery of the giant magnetoresistance. More recently, a new research topic has opened about multiferroic materials in which magnetic and ferroelectric order coexist, both aspects being coupled. With these materials, the processing of information in RAM memories could be achieved through the magnetic and electric polarization (modifying or measuring the local magnetization by applying an electric field, or the local electric polarization with a magnetic field). However, fundamental research remains to be done for understanding the nature of the interactions and mechanisms responsible for the coupling between the two types of order. It is in this context, that recent results were obtained in IRAMIS/SPEC showing that an electric field may influence the magnetism in the BiFeO3 compound.
Potential applications require high-purity, high resistivity multiferroic compounds, with coupled magnetic and electrical order and the highest possible temperatures of order-disorder transitions (magnetic and electric). In that way, the BiFeO3 compound appears highly interesting because it is the only multiferroic oxide with transition temperatures well above room temperature. It was therefore very studied experimentally during the past three years.
G. Lambert1,2,3, T. Hara2,4, D. Garzella1, T. Tanikawa2, M. Labat1,3, B. Carre1, H. Kitamura2,4, T. Shintake2,4, M. Bougeard1, S. Inoue4, Y. Tanaka2,4, P. Salieres1, H. Merdji1, O. Chubar3, O. Gobert1, K. Tahara2, M.-E. Couprie3
1Service des Photons, Atomes et Molécules, DSM/DRECAM, CEA-Saclay, 91191 Gif-sur-Yvette, France
2RIKEN SPring-8 Centre, Harima Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
3Groupe Magnétisme et Insertion, Synchrotron Soleil, L'Orme des Merisiers, Saint Aubin, 91192 Gif-sur-Yvette, France
4XFEL Project Head Office/RIKEN, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
At a time when we question the fossil fuel reserves of our planet and the consequences of the greenhouse effect on global warming, hydrogen is seen as the future energy vector for transportation. Research within CEA cover all stages of this chain: production, storage, transport, distribution and use. In that field, hydrogen produced from primary energy, solar, nuclear, wind, chemical ... is stored in the tank of a vehicle and a fuel cell, allowing the clean conversion (without CO2 emission) of chemical energy into electrical energy, combined with an electric engine can replace the gasoline engine of our cars.
Among the various types of fuel cells suitable for transport applications, the most interesting are of PEMFC type (Proton Exchange Membrane Fuel Cell). These fuel cells contain, in particular, a polymer playing the role of the solid electrolyte. The Dupont De Nemours company sells a sulfonated perfluorocarbon membrane named Nafion®. However, this membrane presents some drawbacks as a mediocre autonomy (< 5000h operating), a mechanical weakness or the inability to function in anhydrous media… The "Irradiated Polymer" research group within LSI is trying to address these problems by proposing a new type of membrane.