Switching Magnetic Ordering by Electric fields in Multiferroics

Multiferroic materials have recently experienced a regain of interest because of their inherent crosscoupling between electric and magnetic degrees of freedom. In particular, a systematic control of themagnitude and crystallographic direction of magnetic order parameters by an electric field is attractivefor the design of original devices. The aim of this Talk is to report the results of ab-initio and firstprinciples-based calculations that predict two different novel ways to achieve such control inmultiferroic BiFeO3 (BFO).1) One way to attain such control is via the existence of an energy term that (i) directly couplesmagnetic moments and electric polarization, P, and (ii) is linear in P. A particular example ofsuch energy term is the spin-current model [1,2,3]. Here, we demonstrate that this term allows anelectric-field-driven and ultrafast switching of the magnetic chirality in the ground state of BFO(that is R3c on a structural point of view and that exhibits a cycloid on a magnetic point of view)[4]. This switching is further found to involve original intermediate magnetic states.2) Another way to control magnetic quantities by an electric field can be thought as being``indirect’’: there is a trilinear ``structural-only'' coupling between polarization and two differentstructural quantities that leads to the reversal of one of these two structural quantities whenswitching the direction of the polarization [5]. Then, this reversal can result in the change ofdirection of a magnetic order parameter, via a second physical energy [6]. Here, we show thatsuch ``indirect’’ magneto-electric coupling can indeed exist in BFO films, and provide theanalytical expression and original physical quantities of these two energies [7].If times allows, other striking magneto-electric effects will also be discussed [8,9,10].References:[1] H. Katsura, N. Nagaosa, and A. V. Balatsky, Physical Review Letters 95, 057205 (2005).[2] D. Rahmedov et al, Physical Review Letters 109, 037207 (2012).[3] A. Raeliarijaona, S. Singh, H. Fu, and L. Bellaiche, Physical Review Letters 110, 137205 (2013).[4] S. Bhattacharjee et al, Physical Review Letters 112, 147601 (2014).[5] N. A. Benedek and C. J. Fennie, Physical Review Letters 106, 107204 (2011).[6] L. Bellaiche et al, Journal of Physics Condensed Matter 24, 312201(2012).[7] Y. Yang et al, Physical Review Letters 112, 057202 (2014).[8] H. J. Zhao et al, Nature Communications 5, 4021 (2014).[9] B. Xu et al, Advanced Functional Materials 25, 552 (2015).[10] B. Xu et al, Advanced Functional Materials 25, 3626 (2015).