  Two fundamental properties of stellar magnetic fields have been determined by
observations for solar-like stars with different Rossby numbers (Ro), namely,
the magnetic field strength and the magnetic cycle period. The field strength
exhibits two regimes: 1) for fast rotation it is independent of Ro, 2) for slow
rotation it decays with Ro following a power law. For the magnetic cycle period
two regimes of activity, the active and inactive branches, also have been
identified. For both of them, the longer the rotation period, the longer the
activity cycle. Using global dynamo simulations of solar like stars with Rossby
numbers between ~0.4 and ~2, this paper explores the relevance of rotational
shear layers in determining these observational properties. Our results,
consistent with non-linear alpha^2-Omega dynamos, show that the total magnetic
field strength is independent of the rotation period. Yet at surface levels,
the origin of the magnetic field is determined by Ro. While for Ro<1 it is
generated in the convection zone, for Ro>1 strong toroidal fields are generated
at the tachocline and rapidly emerge towards the surface. In agreement with the
observations, the magnetic cycle period increases with the rotational period.
However, a bifurcation is observed for Ro~1, separating a regime where
oscillatory dynamos operate mainly in the convection zone, from the regime
where the tachocline has a predominant role. In the latter the cycles are
believed to result from the periodic energy exchange between the dynamo and the
magneto-shear instabilities developing in the tachocline and the radiative
interior.
