Detailed dynamics of a moving magnetic skyrmion lattice in MnSi observed using small-angle neutron scattering under an alternating electric current flow

Moving states of magnetic skyrmions under an alternating current (ac) in MnSi are studied here by small-angle neutron scattering (SANS). A drastic difference is found in the SANS patterns measured with the ac frequency below and above the threshold value, indicating that the viscous motion of skyrmion-lattice domains at low frequencies changes to oscillations of individual skyrmions. These oscillations decrease dislocations of the skyrmion lattice by a random organization effect and, with that, the dislocation density of the skyrmion lattice can be controlled by the ac frequency.