Ferroelectric oxides exhibit intriguing properties and may also support magnetic states leading to so called multiferrroic properties. Ferroelectric as a separate class are making possible non-volatile storage system with high information storage capacities requiring low power. The coupled systems which exhibit both magnetic and ferroelectric behavior materials show promise to lead to devices in which
ferromagnetic memory can be written with magnetic fields or magnetic bits can be written by an electric field. The work conducted in our research focuses on single phase materials. In our previous proposal we studied the detailed coupling of the spin and lattice correlations in these systems. We explored the complex low temperature behavior of hexagonal layered RMnO3 (R= rare earth, Y and Sc) system
following the detailed structural changes which occurred on crossing into the magnetic states. This analysis was extended to the small-ion E-phase systems. The techniques were applied to other layered materials such as superconductors and thermoelectric.
In the next phase, we will complete the work on the small ion perovskite E-phase systems and extend the structural studies down to temperature below10 K, where the total measured polarization rapidly increases and where contact with DFT (T=0) measurements may be made. Moving towards materials with possible device applications, we will examine nano-scale materials as a path toward high
density storage. Detailed measurement of the structural properties and dynamics will be conducted over a range of length scales from atomic to mesoscopic scale using, x-ray absorption spectroscopy, x-ray diffuse scattering, x-ray and neutron pair distribution analysis and high resolution x-ray diffraction. Changes in vibration modes which occur with the onset of polarization will be probed with temperature and pressure dependent infrared absorption spectroscopy. The multiple length scale synchrotron based measurements may assist in developing more detailed models of these materials and possibly lead to device applications. The experimental work will be complemented by density functional methods to determine the magnetic ground states and ab initio molecular dynamics methods (AIMD) to determine the high temperature structures and estimate the electrical polarization given the experimentally derived structures. An important contribution of this work will be the training of graduate students and postdoctoral researchers in materials synthesis and synchrotron based spectroscopy and x-ray scattering techniques. The questions to be addressed are:
1. What are structural (ionic) and electronic contributions to the electric polarization ?
2. As the particle size enters the nano-scale how do the surface and bulk structure change
chemically and structurally?
3. Were there important chemical variations/defects that affect the polarization?
4. How can the polarization amplitude be enhanced?
5. How does pressure modify the electric polarization?