Multiferroics, compounds with both magnetic and ferroelectric orders, are believed to be a key material system to achieve cross-control between magnetism and electricity in a solid with minute energy dissipation. Such a colossal magnetoelectric (ME) effect has been an issue of keen interest for a long time in condensed matter physics as well as a most desired function in the emerging spin-related electronics. Here we begin with the basic mechanisms to realize multiferroicity or spin-driven ferroelectricity in magnetic materials, which have recently been clarified and proved both theoretically and experimentally. According to the proposed mechanisms, many families of multiferroics have been explored, found (re-discovered), and newly developed, realizing a variety of colossal ME controls. We overview versatile multiferroics from the viewpoints of their multiferroicity mechanisms and their fundamental ME characteristics on the basis of the recent advances in exploratory materials. One of the new directions in multiferroic science is the dynamical ME effect, namely the dynamical and/or fast cross-control between electric and magnetic dipoles in a solid. We argue here that the dynamics of multiferroic domain walls significantly contributes to the amplification of ME response, which has been revealed through the dielectric spectroscopy. Another related issue is the electric-dipole-active magnetic resonance, called electromagnons. The electromagnons can provide a new stage of ME optics via resonant coupling with the external electromagnetic wave (light). Finally, we give concluding remarks on multiferroics physics in the light of a broader perspective from the emergent electromagnetism in a solid as well as from the possible application toward future dissipationless electronics.

Multiferroics of spin origin

Cross correlation between magnetism and electricity in a solid can host magnetoelectric effects, such as magnetic (electric) induction of polarization (magnetization) A key to attain the gigantic magnetoelectric response is to find the efficient magnetism–electricity coupling mechanisms Among those, recently the emergence of spontaneous (ferroelectric) polarization in the insulating helimagnet or spiral-spin structure was unraveled, as mediated by the spin-exchange and spin–orbit interactions The sign of the polarization depends on the helicity (spin rotation sense), while the polarization direction itself depends on further details of the mechanism and the underlying lattice symmetry Here, we describe some prototypical examples of the spiral-spin multiferroics, which enable some unconventional magnetoelectric control such as the magnetic-field-induced change of the polarization direction and magnitude as well as the electric-field-induced change of the spin helicity and magnetic domain

http://ir.hfcas.ac.cn:8080/bitstream/334002/4784/1/1554_ftp.pdf

Multiferroics with Spiral Spin Orders

Magnetoelectric multiferroics is an old but emerging class of materials that combine coupled electric and magnetic dipole order. In these materials, ferroelectric and magnetic (ferromagnetic or antiferromagnetic) states coexist or compete with each other. The interaction leads to a so-called magnetoelectric effect, which is the induction of magnetization by an electric field or electric polarization by a magnetic field. In the past few years, a new set of magnetoelectric multiferroics such as TbMnO3 and Ni3V2O8 has been discovered. In these magnetoelectric multiferroics, ferroelectric order develops upon a magnetic phase transition into a spiral magnetic ordered phase. In addition, these systems show large magnetoelectric effects accompanied by metamagnetic transitions. Noncollinear spiral magnetism is the key to understanding the magnetoelectric properties in these systems. Here I discuss the magnetoelectric coupling in spiral magnets and review recent advances in the understanding of ferroelectr...

Spiral Magnets as Magnetoelectrics

A novel type of magnetic origin of ferroelectric polarization is proposed. In crystals with triclinic, monoclinic, or trigonal (rhombohedral) symmetries, the proper screw type of magnetic ordering can induce ferroelectricity through the variation in the metal–ligand hybridization with spin–orbit coupling. The ferroelectric polarization in delafossite compounds Cu(Fe,Al)O 2 is successfully explained by the mechanism. The relation between the polarization direction and the magnetic modulation vector is also predicted.

Ferroelectricity Induced by Proper-Screw Type Magnetic Order

Ferroelectricity Induced by Proper-Screw Type Magnetic Order(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was foun...

H. Aruga Katori

Papers

Field-Induced Magnetic Phase Transitions in a Triangular Lattice Antiferromagnet CuFeO 2 up to 14.5 T