  The effect of magnetic field on the nonlinear growth rate of Rayleigh-Taylor
instability induced two fluid interfacial structures has been investigated. The
magnetic field is assumed to be parallel to the plane of the two fluid
interface and acts in a direction perpendicular to the wave vector. If magnetic
field is restricted only to either side of the interface the growth rate may be
depressed (may almost disappear) or be enhanced depending on whether the
magnetic pressure on the interface opposes the instability driving pressure
difference g({\rho}h - {\rho}l)y or acts in the same direction. If magnetic
field is present on both sides of the two fluid interface, stabilization may
also take place in the sense that the surface of separation undulates
periodically when the force due to magnetic pressure on two sides are such as
to act in opposite direction. This result differs from the classical linear
theory result which predicts that the magnetic field parallel to the surface
has no influence on the growth rate when the wave vector is perpendicular to
its direction.
