Multiferroics of spin origin

Abstract

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.

Emergent functions of quantum materials

“…By contrast, type-II multiferroics inherently host strong ME coupling despite smaller ferroelectric polarization and lower transition temperature 38 . Various types of spin orders can produce ferroelectric P. Three representative mechanisms for spin-order-induced ferroelectricity 39,40 are shown in the upper panel of Fig. 3: symmetric spin exchange interaction e ij (S i · S j ), antisymmetric spin exchange interaction showing the optical magnetoelectric e ect-that is, directional dichroism with respect to oppositely propagating, +k ω versus −k ω , terahertz light beams.…”

“…These models have recently led the development or rediscovery of an increasing number of multiferroics 39 . Among them, the symmetric exchange interaction working between the neighbouring spins, S i and S j , may induce polar striction along the bond direction e ij , as shown in Fig.…”

Magnetic field-temperature phase diagram of multiferroic [(CH3)2NH2]Mn(HCOO)3<

“…Examples include the classic spin flop, 1-6 magnetic saturation transitions, [7][8][9] and those with a sequence of metamagnetic, helical, and nano-pantograph spin states. [10][11][12] The emergent class of tunable multiferroics with chemical formula [(CH 3 ) 2 NH 2 ]M (HCOO) 3 (M = Mn 2+ , Fe 2+ , Ni 2+ , Co 2+ ) provides a number of exciting opportunities in this regard. The Mn analog [(CH 3 ) 2 NH 2 ]Mn(HCOO) 3 is ferroelectric below T C =185 K with polarization P =1.5 µC/cm 2 .…”

Multiferroic Materials: Physics and Properties

“…63 We distinguish different microscopic magnetoelectric coupling mechanisms and discuss the details on the basis of a relevant material. Materials showing improper ferroelectricity, which arises as a consequence of spin order, can be subdivided into three groups based on distinct magnetoelectric coupling mechanisms.…”

“…In some materials, multiple coupling mechanisms are active. For an extensive review on multiferroics of spin origin, we refer the reader to Tokura et al 63 …”