X-Ray and Neutron Scattering Studies of Multiferroics with Ferroelectricity Induced by Spin or Charge Order

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Non-technical:Magnetic and electrical properties of materials are of great technological importance, as well as of fundamental scientific interest. In some materials, there is a coupling between magnetization and electrical polarization (magnets produce magnetic field, while electrically-polarized materials, or ferroelectrics, produce an electric field). These materials are called multiferroics. Multiferroics hold potential for various applications, such as electronics and information storage technologies. Recently, two new classes of multiferroics were discovered. In one class, ferroelectricity results directly from magnetism, and in the other the electrical properties are coupled to magnetism due to strong quantum effects. In the both cases, the magneto-electric coupling is unusually strong (a useful property), but the physics of the coupling is unknown. This project is devoted to investigation of the microscopic origins of the magneto-electric coupling in these materials using x-rays and neutrons. The results will shed light on the new multiferroics, and will help search for new materials with technologically useful properties. In addition, highly-needed specialists for new National research facilities at Oak Ridge, Brookhaven, and other National Laboratories will be trained.Technical:Magnetoelectric (ME) multiferroics are materials in which magnetic and electrical polarizations are coupled to each other. Multiferroics are of scientific interest, and they also hold potential for applications, such as information storage and spintronics. Materials with large ME coupling are rare. Recently, two new classes of multiferroics with unusually large ME coupling were discovered: magnetically-driven multiferroics, and ferroelectrics in which polarization is due to strong electronic correlations (e.g. charge order). The physics of the ME properties in these materials is understood poorly. This project is devoted to investigation of the lattice and magnetic structures of several prominent compound series of new multiferroics: the REMn2O5 system, perovskite manganites with charge order, and ReM2O4 layered magnets. Ferroelectric distortions, magnetic structures, excitations, and effects of magnetic and electric fields on these properties will be investigated using x-ray and neutron scattering. These studies will shed light on the mechanism of the ME effect, and will aid in design of new magnetoelectrics with enhanced properties. Students and postdocs trained under this Project will become specialists in scattering techniques, fulfilling an urgent current need for personnel at newly constructed National facilities at Oak Ridge, Brookhaven, and other National Laboratories. This project will also foster collaboration between regional Universities under the auspices of the recently established Rutgers Center for Emergent Materials.