  Achieving high velocities of magnetic domain walls is a crucial factor for
their use as information carriers in modern nanoelectronic applications. In
nanomagnetism and spintronics, these velocities are often limited either by
internal domain wall instabilities, known as the Walker breakdown phenomenon,
or by spin wave emission, known as the magnonic regime. In the rigid domain
wall model, the maximum magnon velocity acts as an effective "speed of light",
providing a relativistic analogy for the domain wall speed limitation.
Cylindrical magnetic nanowires are an example of systems with the absence of
the Walker breakdown phenomenon. Here we demonstrate that in cylindrical
nanowires with high magnetization such as Iron, also the magnonic limit could
be outstandingly surpassed. Our numerical modelling shows the Bloch point
domain wall velocities as high as 14 km/s, well above the magnonic limit
estimated in the interval 1.7-2.0 km/s. The key ingredient is the conical shape
of the domain wall which elongates and breaks during the dynamics, leading to
domain wall acceleration due to the jet propulsion effect. This effect will be
very important for three-dimensional spintronic networks based on cylindrical
magnetic nanowires.
