A racetrack memory device facilitates the manipulation of a series of
domain walls along the racetrack. The racetrack is designed so that the
domain wall energy increases and decreases in a continuous fashion
between adjacent pinning sites, so that a domain wall does not become
stuck between them. The variation in the domain wall energy along the
racetrack can be provided by continuous variations of the racetrack's
width (while maintaining constant thickness) and/or cross-sectional area
(in which the racetrack dimensions are varied in both directions
perpendicular to the length of the racetrack). Alternatively, this
variation in domain wall energy may be provided by varying the magnetic
properties of the racetrack along the racetrack while otherwise keeping
the shape and size of the racetrack unchanged. In addition, variations of
the racetrack's composition and/or shape can be used.