  Terahertz (THz) magnonics represent the notion of mathematical algebraic
operations of magnons such as addition and subtraction in THz regime which is
an emergent dissipationless ultrafast alternative to existing data processing
technologies. Spin waves on antiferromagnets with a twist in spin order host
such magnons in THz regime, which possess advantage of higher processing
speeds, additional polarization degree of freedom and longer propagation
lengths compared to that of gigahertz magnons in ferromagnets. While
interaction among THz magnons is the crux of algebra operations, it requires
magnetic orders with closely spaced magnon modes for easier experimental
realization of their interactions. Herein, rich wealth of magnons spanning a
narrow energy range of 0.4 to 10 meV is unraveled in Co4Ta2O9 using magneto-THz
spectroscopy. Rare multitude of ten excitation modes, either of magnons or
hybrid magnon-phonon modes is presented. Among other attributes, spin lattice
interaction suggests a correlation among spin and local lattice distortion,
magnetostriction, and magnetic exchange interaction signifying a THz
magnetoelectric effect. This unification of structural, magnetic and dielectric
facets, and their magnetic field control in a narrow spectrum unwinds the
mechanism underneath the system's complexity while the manifestation of
multitude of spin excitation modes is a potential source to design multiple
channels in spin-wave computing based devices.
