Multiferroics are a family of materials in which two properties that do not usually go together coexist: magnetism and ferroelectricity. Magnetism occurs naturally in some materials (such as iron) which have a remanent magnetization, i.e. it remains after the magnetic field is removed. The direction of the remanent magnetization can be reversed by applying an opposite magnetic field, thus providing a memory effect. A ferroelectric compound has electric dipoles which, when aligned by an electric field, generate a polarization, also remanent, which can be reversed by applying an electric field.
Normally, ferroelectricity – and thus multiferroic character – is only found in insulators, but in our recent paper just published in Nature Physics we have discovered a new type of material system that is both ferroelectric and magnetic while being an excellent electrical conductor. This new material is a type of two-dimensional electron gas – a metallic conductor only a few atomic planes thick – formed at the interface between two compounds of the perovskite oxide family. The results of this study show for the first time that ferroelectricity, magnetism and metallicity are found in the same system. Moreover, these three properties are coupled, i.e. acting on one of them affects the others: for example, applying an electric field to reverse the ferroelectric polarization remanently modifies the electrical resistance of the electron gas. Its electronic transport properties are also modulated by its magnetic properties, all of which are controlled by the direction of the ferroelectric polarization. The coexistence of these properties and the possibility to control them easily with an electrical voltage opens the way to new devices for information storage and low energy computing.
This work was a collaboration with CNR-SPIN in Naples, the University Federico II of Naples, the Paul Scherrer Institute and CRISMAT in Caen.
J. Bréhin, Y. Chen, M. D’Antuono, S. Varotto, D. Stornaiuolo, C. Piamonteze, J. Varignon, M. Salluzzo and M. Bibes
Coexistence and coupling of ferroelectricity and magnetism in an oxide two-dimensional electron gas
Nature Phys. doi:10.1038/s41567-023-01983-y (2023)
See also the news piece on the website of CNRS Institute of Physics (in French).