  Magnetic monopoles have provided a rich field of study, leading to a wide
area of research in particle physics, solid state physics, ultra-cold gases,
superconductors, cosmology, and gauge theory. So far, no true magnetic
monopoles were found experimentally. Using the Aharonov-Bohm effect, one of the
central results of quantum physics, shows however, that an effective monopole
field can be produced. Understanding the effects of such a monopole field on
its surroundings is crucial to its observation and provides a better grasp of
fundamental physical theory. We realize the diffraction of fast electrons at a
magnetic monopole field generated by a nanoscopic magnetized ferromagnetic
needle. Previous studies have been limited to theoretical semiclassical optical
calculations of the motion of electrons in such a monopole field. Solid state
systems like the recently studied 'spin ice' provide a constrained system to
study similar fields, but make it impossible to separate the monopole from the
material. Free space diffraction helps to understand the dynamics of the
electron-monopole system without the complexity of a solid state system. The
use of a simple object such as a magnetized needle will allow various areas of
physics to use the general dynamical effects of monopole fields without
requiring a monopole particle or specific solids which have internal
monopole-like properties. The experiment performed here shows that even without
a true magnetic monopole particle, the theoretical background on monopoles
serves as a basis for experiments and can be applied to efficiently create
electron vortices. Various predictions about angular momentum and general field
effects can readily be studied using the available equipment. This realization
provides insights for the scientific community on how to detect magnetic
monopoles in high energy collisions, cosmological processes, or novel
materials.
