  The dynamics and stability of magnetic skyrmions within a nano-track with
multiple confinements are investigated. Firstly, the motion of a single
skyrmion under spin transfer torque (STT) is studied. By accurately adjusting
the current pulse magnitude and width, the study reveals the possibility to pin
and stabilize the skyrmion in each confinement. Due to the Hall angle, the
depining of the skyrmion from the top confinement requires two pulses with
adjustable time delay while a single pulse is enough to depin it for the case
of bottom confinement. In the case of two skyrmions, once one is pinned in one
confinement, the second one stabilizes in the nearest available empty state and
no more than one skyrmion could be seen in single confinement. Finally and for
further confirmation of this behavior, the motion of a large number of
skyrmions is investigated under the same conditions. The results show that a
multistate device could be obtained with still the existence of only one
skyrmion per state. The skyrmions could be displaced along the nano-track until
their annihilation at the end of the device.
