  Terahertz driven magnetization dynamics are explored in the orthoferrite
DyFeO3. A high-field, single cycle THz pulse is used to excite magnon modes in
the crystal together with other resonances. Both quasi-ferromagnetic and
quasi-antiferromagnetic magnon modes are excited and appear in time-resolved
measurements of the Faraday rotation. Other modes are also observed in the
measurements of the time-resolved linear birefringence. Analysis of the
excitation process reveals that despite larger than expected electro-optical
susceptibility it is mainly the THz magnetic field that couples to the
quasi-ferromagnetic and quasi-antiferromagnetic magnon branches.
