  The observed distribution of radii for exoplanets shows a bimodal form that
can be explained by mass-loss from planetary atmospheres due to high energy
radiation emitted by their host stars. The location of the minimum of this
radius distribution depends on the mass-radius relation, which in turn depends
on the composition of planetary cores. Current studies suggest that super-Earth
and mini-Neptune planets have iron-rich and hence largely Earth-like
composition cores. This paper explores how non-zero planetary magnetic fields
can decrease the expected mass-loss rates from these planets. These lower
mass-loss rates, in turn, affect the location of the minimum of the radius
distribution and the inferred chemical composition of the planetary cores.
