  In this paper we establish a connection between the bulk topological
structure and the magnetic properties of drumhead surface states of nodal loop
semimetals. We identify the magnetic characteristics of the surface states and
compute the system's magnon spectrum by treating electron-electron interactions
on a mean-field level. We draw attention to a subtle connection between a
Lifshitz-like transition of the surface states driven by mechanical distortions
and the magnetic characteristics of the system. Our findings may be
experimentally verified e.g. by spin polarized electron energy loss
spectroscopy of nodal semimetal surfaces.
