Giant Spin-induced Polarization and Optical-diode effect by electromagnons in BiFeO3

Abstract

Type-I multiferroics where spin and electric polarization order at distinct temperatures were believed to have smaller couplings between them compared to type-\textit{II} multiferroics such as TbMnO3. However, we recently discovered unexpectedly huge couplings between spin and electric polarization in representative type-I multiferroic BiFeO3. This hidden coupling leads to record-high spin-induced ferroelectric polarizations (\textasciitilde 3.0 μC/cm2) [1] which is one or two order larger than in any other multiferroics. Also, the spin-polarization couplings in \textit{dynamic} region [2] generates strong electromagnons resulting in sizable one-way optical transparency at the spin-wave excitations [3]. Overall, we show how our theoretical results revive studies in revealing hidden but huge spin-polarization couplings and their dynamic interactions with light in type-I multiferroics.