  A next-generation memory device utilizing a three-dimensional nanowire system
requires the reliable control of domain wall motion. In this letter, domain
walls are studied in cylindrical nanowires consisting of alternating segments
of cobalt and nickel. The material interfaces acting as domain wall pinning
sites, are utilized in combination with current pulses, to control the position
of the domain wall, which is monitored using magnetoresistance measurements.
Magnetic force microscopy results further confirm the occurrence of current
assisted domain wall depinning. Data bits are therefore shifted along the
nanowire by sequentially pinning and depinning a domain wall between successive
interfaces, a requirement necessary for race-track type memory devices. We
demonstrate that the direction, amplitude and duration of the applied current
pulses determine the propagation of the domain wall across pinning sites. These
results demonstrate a multi-bit cylindrical nanowire device, utilizing current
assisted data manipulation. The prospect of sequential pinning and depinning in
these nanowires allows the bit density to increase by several Tbs, depending on
the number of segments within these nanowires.
