Giant gigahertz optical activity in multiferroic ferroborate

Abstract

In contrast to well studied multiferroic manganites with a spiral structure, the electric polarization in multiferroic borates is induced within collinear antiferromagnetic structure and can easily be switched by small static fields. Because of specific symmetry conditions, static and dynamic properties in borates are directly connected, which leads to giant magnetoelectric and magnetodielectric effects. Here we prove experimentally that the giant magnetodielectric effect in samarium ferroborate SmFe3(BO3)4 is of intrinsic origin and is caused by an unusually large electromagnon situated in the microwave range. This electromagnon reveals strong optical activity exceeding 120 degrees of polarization rotation in a millimeter thick sample

Far-IR magnetospectroscopy of magnons and electromagnons in TbFeO3 single crystals at low temperatures

“…[28,29,30]. The current interest to electromagnons is due to their non-trivial optical properties, such as directional dichroism [31,32] and giant optical activity [33], and promising new functionalities, such as magnetically controlled directional light switches [34] and control of magnetism on a sub-picosecond time scale [35]. The main microscopic mechanisms driving electric dipole-activity of magnetic excitations are considered to be symmetric exchange striction [36], antisymmetric exchange interaction in the frame of a spin-current model [37] and spin-dependent p−d hybridization [38].…”

Terahertz spectroscopy of crystal-field transitions in magnetoelectric TmAl3(BO3)4

“…Rare earth borates [1,2] thus represent a new class of multiferroic materials [5,6] with non-centrosymmetric crystal structure. These compounds have trigonal structure (space group R32 or P3 1 21) of natural mineral huntite [7] and consist of helicoidal chains of edge-sharing FeO 6 octahera along the trigonal c-axis, interconnected by BO 3 triangles and RO 6 prisms (upper panel of Fig. 1).…”

Switching of Magnons by Electric and Magnetic Fields in Multiferroic Borates

“…Multiferroic iron borates present a rich collection of excitations in the terahertz range [62][63][64][65]. According the optical experiments [66,67], in the iron borates the splitting of the ground rare-earth doublets are close to the magnon frequencies of the magnetic Fe-subsystem.…”

“…In magnetoelectric ferroborates the process includes both, rotation of the magnetic moments and switching of the electric polarization. The characteristic time scale for the magnetic part is determined by the in-plane antiferromagnetic resonance frequency (∼ 5 GHz at H = 0) [64], which will probably determine the switching rate. Finally, for short pulses, electric and magnetic fields are present simultaneously.…”

“…In case of SmFe 3 (BO 3 ) 4 other modes [62] may be also expected to reveal voltage sensitivity. For the low-frequency electromagnon [64,65] strong static magnetic field must be applied to raise the resonance frequency up to the millimeter frequency range. Magnetic field thus would align the Fe moments (see Fig.…”