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Multiferroics have been formally defined as materials that exhibit more than one primary ferroic order parameter simultaneously (i.e. in a single phase), and many researchers in the field consider materials to be multiferroics only if they exhibit coupling between primary order parameters. However, the definition of multiferroics can be expanded to include non-primary order parameters, such as antiferromagnetism or ferrimagnetism. The four basic primary ferroic order parameters are #ferromagnetism #ferroelectricity #ferroelasticity #ferrotoroidicity The last is a topic of some debate, as there was no evidence for switching ferrotoroidicity until recently. Many multiferroics are transition metal oxides with perovskite crystal structure, and include rare-earth manganites and -ferrites (e.g. TbMnO3, HoMn2O5, LuFe2O4 and recently, "PZTFT",). Other examples are the bismuth compounds BiFeO3 and BiMnO3, non-perovskite oxide LiCu2O2, and non-oxides such as BaNiF4 and spinel chalcogenides, e.g. ZnCr2Se4. These alloys show rich phase diagrams combining different ferroic orders in separate phases. Apart from single phase multiferroics, composites and heterostructures exhibiting more than one ferroic order parameter are studied extensively. Some examples include magnetic thin films on piezoelectric PMN-PT substrates and Metglass/PVDF/Metglass trilayer structures. Besides scientific interest in their physical properties, multiferroics have potential for applications as actuators, switches, magnetic field sensors or new types of electronic memory devices. ==History== The term multiferroic was first used by H. Schmid in 1994. His definition referred to multiferroics as single phase materials which simultaneously possess two or more primary ferroic properties. Today the term multiferroic has been expanded to include materials which exhibit any type of long range magnetic ordering, spontaneous electric polarization, and/or ferroelasticity. Working under this expanded definition the history of magnetoelectric multiferroics can be traced back to the 1960s. In the most general sense the field of multiferroics was born from studies of magnetoelectric systems. After an initial burst of interest, research remained static until early 2000 (see figure). In 2003 the discovery of large ferroelectric polarization in epitaxially grown thin films of BiFeO3 and the discovery of strong magnetic and electric coupling in orthorhombic TbMnO3 and TbMn2O5 re-stimulated activity in the field of multiferroics. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Multiferroics」の詳細全文を読む スポンサード リンク
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