Deterministic control of an antiferromagnetic spin arrangement using ultrafast optical excitation

A central prospect of antiferromagnetic spintronics is to exploit magnetic properties that are unavailable with ferromagnets. However, this poses the challenge of accessing such properties for readout and control. To this end, light-induced manipulation of the transient ground state, e.g. by changing the magnetic anisotropy potential, opens promising pathways towards ultrafast deterministic control of antiferromagnetism. Here, we use this approach to trigger a $it{coherent}$ rotation of the entire long-range antiferromagnetic spin arrangement about a crystalline axis in $GdRh_2Si_2$ and demonstrate $it{deterministic}$ control of this rotation upon ultrafast optical excitation. Our observations can be explained by a displacive excitation of the Gd spins$$ local anisotropy potential by the optical excitation, allowing for a full description of this transient magnetic anisotropy potential.