Multiferroic materials and magnetoelectric physics: symmetry, entanglement, excitation, and topology

Abstract

Multiferroics are those materials with more than one ferroic order, and magnetoelectricity refers to the mutual coupling between magnetism (spins and/or magnetic field) and electricity (electric dipoles and/or electric field). In spite of the long research history in the whole twentieth century, the discipline of multiferroicity has never been so highly active as that in the first decade of the twenty-first century, and it has become one of the hottest disciplines of condensed matter physics and materials science. A series of milestones and steady progress in the past decade have enabled our understanding of multiferroic physics substantially comprehensive and profound, which is further pushing forward the research frontier of this exciting area. The availability of more multiferroic materials and improved magnetoelectric performance are approaching to make the applications within reach. While seminal review articles covering the major progress before 2010 are available, an updated review addressing the new achievements since that time becomes imperative. In this review, following a concise outline of the basic knowledge of multiferroicity and magnetoelectricity, we summarize the important research activities on multiferroics, especially magnetoelectricity and related physics in the last six years. We consider not only single-phase multiferroics but also multiferroic heterostructures. We address the physical mechanisms regarding magnetoelectric coupling so that the backbone of this divergent discipline can be highlighted. A series of issues on lattice symmetry, magnetic ordering, ferroelectricity generation, electromagnon excitations, multiferroic domain structure and domain wall dynamics, and interfacial coupling in multiferroic heterostructures, will be revisited in an updated framework of physics. In addition, several emergent phenomena and related physics, including magnetic skyrmions and generic topological structures associated with magnetoelectricity will be discussed. The review is ended with a set of prospectives and forward-looking conclusions, which may inevitably reflect the authors' biased opinions but are certainly critical.

Keywords:

• Time-reversal and space-inversion symmetries
• multiferroicity and magnetoelectricity
• spin–orbit coupling
• electromagnon
• skyrmion
• ferroelectric domain
• ferroelectric field effect
• exchange bias

PACS:

• 75.85.+t magnetoelectric effects
• multiferroics
• 77.55.Nv multiferroic/magnetoelectric films
• 77.80.-e ferroelectricity and antiferroelectricity
• 75.70.Tj spin–orbit effects
• 75.80.+q magnetomechanical effects
• magnetostriction

Acknowledgements

We thank E. Dagotto, Y.H. Chu, X.G. Li, H.J. Xiang, Y.S. Chai, P. Yu, among many others, for helpful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This work was partially supported by the National Natural Science Foundation of China (grant numbers 51322206, 11234005, 11274060, 51431006, 51332006), the National 973 Projects of China (grant number 2015CB654602), the Jiangsu Key Laboratory for Advanced Metallic Materials (grant number BM2007204). S.W.C. is supported in part by the Department of Energy under grant number DE-FG02-07ER46382, and also by the Visiting Distinguished Professorship of Nanjing University sponsored by the State Administration of Foreign Experts Affairs of China. The work performed at the University of Houston is funded the Department of Energy, Basic Energy Science, under grant number DE-FG02-13ER46917/DE-SC0010831.