Coalescing compact binaries are the strongest gravitational wave emitters detectable by latest network of ground-based detectors that are ready to make detections beginning this year. However, in order to effectively localize the source of a gravitational wave signal as well as determine the parameters of the source and its environment, an electromagnetic counterpart is necessary. At present, there is convincing evidence that short gamma-ray bursts (sGRBs) are emitted by a compact binary merger, rendering it a promising electromagnetic counterpart for an impending gravitational signal. In this light, this work focuses on black hole-neutron star (BHNS) mergers as a viable site of sGRBs. More specifically, the work seeks to understand the role of the magnetic field of the neutron star companion in generating an sGRB. We use numerical relativity to study the magneto-rotational instability (MRI) as a viable magnetic field amplification mechanism in a BHNS merger and determine the possible outcomes that will render a BHNS merger as a promising sGRB site. We find that a large-scale poloidal field, which is necessary to collimate an sGRB jet, is likely generated via the MRI in the outer regions of the accretion disk of the black hole remnant.