Large-amplitude spin dynamics driven by a THz pulse in resonance with an electromagnon

With femtosecond time resolution, x-ray diffraction offers unique capabilities to observe directly the dynamics of long range order. When the x-ray energy is tuned near a core-level transition is is possible in many systems to selectively study the dynamics of long-range order of valence properties such as orbital ordering or magnetic spin. Here I discuss show how resonantly enhanced magnetic scattering can be used to quantitatively measure the character and magnitude of spin motion in a coherent electromagnon in TbMnO$_3$ driven by a THz frequency electromagnetic field. We observe a $4^\circ$ rotation of the antiferromagnetically ordered spin spiral plane, a result consistent with a previously published model that suggests this may be a viable route for ultrafast domain switching in multiferroics.