  Magnetic skyrmions are localized chiral spin textures, which offer great
promise to store and process information at the nanoscale. In the presence of
asymmetric exchange interactions, their chirality, which governs their
dynamics, is generally considered as an intrinsic parameter set during the
sample deposition. In this work, we experimentally demonstrate that a gate
voltage can control this key parameter. We probe the chirality of skyrmions and
chiral domain walls by observing the direction of their current-induced motion
and show that a gate voltage can reverse it. This local and dynamical reversal
of the chirality is due to a sign inversion of the interfacial
Dzyaloshinskii-Moriya interaction that we attribute to ionic migration of
oxygen under gate voltage. Micromagnetic simulations show that the chirality
reversal is a continuous transformation, in which the skyrmion is conserved.
This control of chirality with 2 - 3 V gate voltage can be used for
skyrmion-based logic devices, yielding new functionalities.
