Rare Earth Hexagonal Ferrites: a New Family of Multiferroics

In the quest for new types of information processing and storage, complex oxides stand out as one of the most promising material classes. Multiple functionalities of complex oxides naturally arise from the delicate energy balance between the various forms of orders (structural, electronic, magnetic). In particular, multiferroic oxides which simultaneously exhibit more than one type of ferroic order have many advantages over other existing materials. Wide spread practical applications will require a multiferroic material with a transition temperature that lies considerably above room temperature, large electric and magnetic polarizations, and strong coupling between ferroic orders, which unfortunately has not been realized in a single phase material. In this talk, I will give a brief review of the concept, known mechanism and application of multiferroics in the context of single phase complex oxides. I will also discuss the research on multiferroic materials including tuning known multiferroic materials to achieve desirable properties; 1) discovering new multiferroic materials, and 2) elucidating the underlying mechanism of multiferroicity. The prototypical multiferroic materials hexagonal rare earth ferrites will be employed as examples.