  The aim of this study is to explore the magnetic and flow properties of fully
convective M dwarfs as a function of rotation period Prot and magnetic Reynolds
ReM and Prandlt numbers PrM. We performed three-dimensional simulations of
fully convective stars using a star-in-a-box setup. This setup allows global
dynamo simulations in a sphere embedded in a Cartesian cube. The equations of
non-ideal magnetohydrodynamics were solved with the Pencil Code. We used the
stellar parameters of an M5 dwarf with 0.21M_odot at three rotation rates
corresponding to rotation periods (Prot): 43, 61 and 90 days, and varied the
magnetic Prandtl number in the range from 0.1 to 10. We found systematic
differences in the behaviour of the large-scale magnetic field as functions of
rotation and PrM. For the simulations with Prot = 43 days and PrM <= 2, we
found cyclic large-scale magnetic fields. For PrM > 2 the cycles vanish and
field shows irregular reversals. In simulations with Prot = 61 days for PrM <=
2 the cycles are less clear and the reversal are less periodic. In the
higher-PrM cases, the axisymmetric mean field shows irregular variations. For
the slowest rotation case with Prot = 90 days, the field has an important
dipolar component for PrM <= 5. For the highest PrM the large-scale magnetic
field is predominantly irregular at mid-latitudes, with quasi-stationary fields
near the poles. For the simulations with cycles, the cycle period length
slightly increases with increasing ReM.
