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Magnetism, charge order and ferroelectricity in ternary oxides
Oak Ridge National Laboratory, Solid State Division, Oak Ridge, TN, United States
Magnetic materials are well known for applications e.g. in data storage, but ferroelectric materials have important applications as well, such as being used for sensors. For a material combining both magnetism and ferroelectricity a number of additional applications may be envisaged. Unfortunately, "conventional" ferroelectricity and magnetism seem to be diametrically opposed, and in the rare instances when they occur simultaneously the coupling between magnetic and electric order parameters is weak. Recently, ferroelectricity originating from certain spiral magnetic structures has been observed and described. These materials exhibit a large magneto-electric coupling, but due to the key role of the Dzyaloshinskii-Moriya interaction the ferroelectric polarization is small.An alternative ferroelectric mechanism, allowing in principle for both large polarization and a large magneto-electric coupling, is a suitable charge-ordering. Such a mechanism has been proposed for LuFe2O4. The problem with this compound is that it forms with varying oxygen content. As will be shown, both charge order and magnetic properties depend heavily on the oxygen stoichiometry. More generally, it is important to understand charge-ordered materials. A compound for which (as for LuFe2O4) an electrostatically driven charge-order has been found is Fe2OBO3. This material has been shown to exhibit charge-order, but the structure of the charge-ordering is unclear. The synthesis of single crystals of Fe2OBO3 allowed us to study this compound in greater detail, and results from, among others, Mossbauer and electron microscopy, will be presented. A number of materials with a magnetic mechanism of ferroelectricity will be discussed as well.
Presentation: Invited oral at E-MRS Fall Meeting 2006, Symposium K, by Manuel Angst
See On-line Journal of E-MRS Fall Meeting 2006
Submitted: 2006-05-15 21:07 Revised: 2009-06-07 00:44