Search for a new phase of multiferroic ferroelectric RFe2O4 aimed at practical applications

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In search of multiferroiciity at room temperature, we have conducted the research work on electronic ferroelectric RFe2O4 (R: rare earths). The magnetic transition temperature was not drastically changed by a few kinds of attempts, such as R- and Fe-sites substitutions. However, it was found that the related system R2Fe3O7 shows a magnetic transition at 270 K, which is 20 K higher than that of RFe2O4. As R2Fe3O7 was reported to be ferroelectric at room temperature, this system is multiferroic below 270 K. This result offers a possible increase in transition temperature up to room temperature. In addition, we have revealed several new phenomena of RFe2O4, such as exchange bias and enhancement anisotropy induced by electrical current, which may be used to fabricate new multiferroic devices.