  The magnetization reversal of three-segment cylindrical nanoelements
comprising of alternating nanowire and nanotube sections is investigated by
means of Monte Carlo simulations. Such nanoelements may feature a three-state
behaviour with an intermediate plateau in the hysteresis curve due to a
metastable pinning of the domain walls at the wire-tube interfaces. It turns
out that vortex as well as transverse domain walls contribute to the
magnetization reversal. By varying the geometric parameters, the sequence, or
the material of the elements the nucleation location of domain walls, as well
as their nucleation field, can be tailored. Especially interesting is the novel
possibility to drive domain walls coherently in the same or in opposite
directions by changing the geometry of the hybrid nanoelement. This important
feature adds additional flexibility to the construction of logical devices
based on domain wall movement. Another prominent outcome is that domain walls
can be nucleated near the centre of the element and then traverse to the outer
tips of the cylindrical structure when the applied field is increased, which
also opens the possibility to use these three-segment nanoelements for the
field induced delivery of domain walls as substitutes for large nucleation
pads.
