  Baryon density and magnetic field effect on chaos for the holographic dual of
a $Q \bar Q$ system at finite temperature is studied. A string in an AdS
Reissner Nordstrom background, and in a metric with magnetic field near the
black hole horizon is considered and small time-dependent perturbations of the
static configurations are investigated. The proximity to the horizon induces
chaos, which is softened increasing the chemical potential or the magnetic
field. A background geometry including the effect of a dilaton is also
examined. The Maldacena, Shenker, and Stanford bound on the Lyapunov exponents
characterizing the perturbations is satisfied for finite baryon chemical
potential and magnetic field and when the dilaton is included in the metric.
