  An important vision of modern magnetic research is to use antiferromagnets as
controllable and active ultrafast components in spintronic devices. Hematite is
a promising model material in this respect because its pronounced
Dzyaloshinskii-Moriya interaction leads to the coexistence of
antiferromagnetism and weak ferromagnetism. Here, we use femtosecond laser
pulses to drive terahertz spin currents from hematite into an adjacent Pt
layer. We find two contributions to the generation of the spin current with
distinctly different dynamics: the impulsive stimulated Raman scatting that
relies on the antiferromagnetic order and the ultrafast spin Seebeck effect
that relies on the net magnetization. The total THz spin current dynamics can
thus be manipulated by a medium-strength magnetic field. The controllability of
the THz spin current achieved in hematite opens the pathway toward controlling
the exact spin current dynamics from ultrafast antiferromagnetic spin sources.
