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 n...

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

Multiferroics are those materials with more than one ferroic order, and magnetoelectricity refers to the mutual coupling between magnetism and electricity. 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 phenomenon of negative magnetization and its implications

Hydrothermal synthesis and magnetic properties of multiferroic rare-earth orthoferrites

The crystal and magnetic structures of single-crystalline hexagonal LuFeO(3) films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO(3) films are room-temperature multiferroics.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1017&context=physicsxu

Room-temperature multiferroic hexagonal LuFeO3 films.

Multiferroics have received a great deal of attention because of their fascinating physics of order-parameter cross-couplings and their potential for enabling new device paradigms. Considering the rareness of multiferroic materials, we have been exploring the possibility of artificially imposing ferroelectricity by structurally tailoring antiferromagnets in thin-film forms. YbFeO3 (YbFO hereafter), a family of centrosymmetric rare-earth orthoferrites, is known to be nonferroelectric (space group Pnma). Here we report that a YbFO thin-film heterostructure fabricated by adopting a hexagonal template surprisingly exhibits nonferroelastic ferroelectricity with the Curie temperature of 470 K. The observed ferroelectricity is further characterized by an extraordinary two-step polarization decay, accompanied by a pronounced magnetocapacitance effect near the lower decay temperature, ∼225 K. According to first-principles calculations, the hexagonal P63/mmc–P63mc–P63cm consecutive transitions are primarily respons...

Structurally Tailored Hexagonal Ferroelectricity and Multiferroism in Epitaxial YbFeO3 Thin-Film Heterostructures

Temperature-induced Magnetization Reversal and Ultra-fast Magnetic Switch at Low Field in SmFeO3

Epitaxially Constrained Hexagonal Ferroelectricity and Canted Triangular Spin Order in LuFeO3 Thin Films

Artificially imposed hexagonal ferroelectricity in canted antiferromagnetic YFeO3 epitaxial thin films

TmFeO3 is known to have an orthorhombic structure characterized by the corner-linked FeO6 octahedra in a three-dimensional network (space group Pnma) Thus, it is expected to be non-ferroelectric In the present study, however, we have stabilized a hexagonal TmFeO3 thin-film heterostructure by adopting hexagonal templates In this way, we are able to artificially impose multiferroism on the epitaxially grown TmFeO3 film below 120 K

Suk-Jin Ahn

Papers

Structurally Tailored Hexagonal Ferroelectricity and Multiferroism in Epitaxial YbFeO3 Thin-Film Heterostructures

Temperature-induced Magnetization Reversal and Ultra-fast Magnetic Switch at Low Field in SmFeO3

Epitaxially Constrained Hexagonal Ferroelectricity and Canted Triangular Spin Order in LuFeO3 Thin Films

Artificially imposed hexagonal ferroelectricity in canted antiferromagnetic YFeO3 epitaxial thin films

Multiferroism in hexagonally stabilized TmFeO3 thin films below 120 K