  We predict a novel twisted skyrmion structure at the boundary of two
antiferromagnetically coupled magnetic domains with antiparallel magnetization
directions. Through this intermediate state, skyrmions with opposite polarities
can be freely switched between each other by spin-polarized electric currents.
Based on these findings, we propose the concept of double-track skyrmion
racetrack memory and logic gates where the binary data are represented by
skyrmions with different polarities. The dynamics of skyrmion polarity reversal
is theoretically studied. Using the method of image, we derive the analytical
formula of the repulsive potential when a normal skyrmion approaches the domain
boundary. A harmonic attractive potential well is obtained for the twisted
skyrmion across the boundary. Micromagnetic simulations compare well with
theoretical predictions. The method of image skyrmion proposed in this work can
be used to deal with a large class of skyrmion-boundary interaction problems.
