Multiferroicity: the coupling between magnetic and polarization orders

• Published in: Advances in physics 2009-07, Vol.58 (4), p.321-448
• Main Authors: Wang, K.F., Liu, J.-M., Ren, Z.F.
• Format: Article
• Language: English
• Subjects: charge-ordered state; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectrics, piezoelectrics, and ferroelectrics and their properties; electromagnon; Electronic transport in condensed matter; Exact sciences and technology; ferroelectricity; Ferroelectricity and antiferroelectricity; ferrotoroidicity; helical spin-ordered state; Magnetic properties and materials; magnetism; magnetization; magnetoelectric coupling; Magnetomechanical and magnetoelectric effects, magnetostriction; multiferroicity; multiferroics; Physics; polarization; spatial-inversion symmetry breaking; Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.); Spin polarized transport; time-reversion symmetry breaking
• ISSN: 0001-8732; 1460-6976
• DOI: 10.1080/00018730902920554

Multiferroics, defined for those multifunctional materials in which two or more kinds of fundamental ferroicities coexist, have become one of the hottest topics of condensed matter physics and materials science in recent years. The coexistence of several order parameters in multiferroics brings out novel physical phenomena and offers possibilities for new device functions. The revival of research activities on multiferroics is evidenced by some novel discoveries and concepts, both experimentally and theoretically. In this review, we outline some of the progressive milestones in this stimulating field, especially for those single-phase multiferroics where magnetism and ferroelectricity coexist. First, we highlight the physical concepts of multiferroicity and the current challenges to integrate the magnetism and ferroelectricity into a single-phase system. Subsequently, we summarize various strategies used to combine the two types of order. Special attention is paid to three novel mechanisms for multiferroicity generation: (1) the ferroelectricity induced by the spin orders such as spiral and E-phase antiferromagnetic spin orders, which break the spatial inversion symmetry; (2) the ferroelectricity originating from the charge-ordered states; and (3) the ferrotoroidic system. Then, we address the elementary excitations such as electromagnons, and the application potentials of multiferroics. Finally, open questions and future research opportunities are proposed.