Magnetoelastoelectric coupling in core–shell nanoparticles enabling directional and mode-selective magnetic control of THz beam propagation

Magnetoelastoelectric coupling in an engineered biphasic multiferroic nanocomposite enables a novel magnetic field direction-defined propagation control of terahertz (THz) waves. These core-shell nanoparticles are comprised of a ferromagnetic cobalt ferrite core and a ferroelectric barium titanate shell. An assembly of these nanoparticles, when operated in external magnetic fields, exhibits a controllable amplitude modulation when the magnetic field is applied antiparallel to the THz wave propagation direction; yet the same assembly displays an additional phase modulation when the magnetic field is applied along the propagation direction. While field-induced magnetostriction of the core leads to amplitude modulation, phase modulation is a result of stress-mediated piezoelectricity of the outer ferroelectric shell.