  We study drag-driven instability in a protoplanetary disc consisting of a
layer of single-sized dust particles which are coupled to the magnetized gas
aerodynamically and the particle-to-gas feedback is included. We find a
dispersion relation for axisymmetric linear disturbances and growth rate of the
unstable modes are calculated numerically. While the secular gravitational
instability in the absence of particle-to-gas feedback predicts the dust layer
is unstable, magnetic fields significantly amplifies the instability if the
Toomre parameter for the gas component is fixed. We also show that even a weak
magnetic field is able to amplify the instability more or less irrespective of
the dust-gas coupling.
