  The merger of two neutron stars (NSs) produces the emission of gravitational
waves, the formation of a compact object surrounded by a dense and magnetized
environment, and the launching of a collimated and relativistic jet, which will
eventually produce a short gamma-ray burst (SGRB). The interaction of the jet
with the environment has been shown to play a major role in shaping the
structure of the outflow that eventually powers the gamma-ray emission. In this
paper, we present a set of 2.5 dimensional RMHD simulations that follow the
evolution of a relativistic non-magnetized jet through a medium with different
magnetization levels, as produced after the merger of two NSs. We find that the
predominant consequence of a magnetized ambient medium is that of suppressing
instabilities within the jet, and preventing the formation of a series of
collimation shocks. One implication of this is that internal shocks lose
efficiency, causing bursts with low-luminosity prompt emission. On the other
hand, the jet-head velocity and the induced magnetization within the jet are
fairly independent from the magnetization of the ambient medium. Future
numerical studies with a larger domain are necessary to obtain light curves and
spectra in order to better understand the role of magnetized media.
