A strong ferroelectric ferromagnet created via spin-lattice coupling

Magnetoelectric multiferroics are materials, which exhibit simultaneously magnetic and ferroelectric order. Unfortunately, there are only few multiferroics in nature and they have usually low critical temperatures and their magnetoelectric coupling is small. In this paper we first time experimentally demonstrated that new "artificial" multiferroics can be prepared using the strain in the thin films. We proved that originally antiferromagnetic and paraelectric EuTiO₃ changes in strained films to strong ferromagnet and ferroelectrics due to strong spin-lattice coupling. Such system should exhibit strong magnetoelectric coupling which can be used in future memories. Our colleagues from USA prepared the thin films and characterized their crystal structure and magnetic properties. We discovered the ferroelectric phase transition. Without our contribution the paper could not have been accepted in Nature.

Predicted effect of biaxial strain on EuTiO³ and our approach to imparting such strain in EuTiO₃ films using epitaxy. (a) First-principles epitaxial phase diagram of EuTiO₃ strained from −2% (biaxial compression) to +2% (biaxial tension), calculated in 0.1% steps. Regions with paraelectric (PE), ferroelectric (FE), antiferromagnetic (AFM) and ferromagnetic (FM) behaviour are shown. b, c, Schematic of unstrained bulk EuTiO₃ (b) and epitaxially strained thin-film EuTiO₃ on the DyScO₃ substrate (c), showing the in-plane expansion due to biaxial tension.

¹Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853-1501, USA
²Department of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania 16802-5005, USA
³Department of Physics, Ohio State University, Columbus, Ohio 43210-1117, USA
⁴Department of Physics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
⁵School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
⁶Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
⁷Institute of Bio and Nanosystems, JARA-Fundamentals of Future Information Technologies, Research Centre Jülich, D-52425 Jülich, Germany
⁸Institute of Physics ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
⁹Leibniz Institute for Crystal Growth, Max-Born-Straße 2, D-12489 Berlin, Germany
¹⁰Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA
¹¹Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, USA