  In a variety of rare-earth based compounds singlet superconductivity coexists
with helical magnetism. Here we demonstrate that surfaces of these systems
should generically host a finite density of zero-energy Majorana modes. In the
limit of vanishing disorder, these modes lead to a divergent contribution to
zero-energy density of states and to zero-temperature entropy proportional to
the sample surface area. When confined to a wire geometry, a discrete number of
Majorana modes can be isolated. The relatively large characteristic energy
scales for superconductivity and magnetism, compared to other proposals, as
well as the lack of need for fine-tuning, make helical magnetic superconducting
compounds favorable for the observation and experimental investigation of
Majorana fermions.
