  The reversal of magnetisation has been studied in a three dimensional Ising
ferromagnet by Monte Carlo simulation with Metropolis single spin flip
algorithm using random updating scheme. The outer layers are considered as
surface. The surface interacts with core with a relative ferromagnetic
interaction strength. Depending on the relative interaction strength, the time
of reversal of the surface was found to be different from that of the bulk. For
weaker relative strength, surface reversal was found to be faster than that of
bulk and vice versa for stronger relative interaction strength. A critical
value ($R_c$) of relative interaction strength provides same time of reversal
of surface and bulk. This critical relative interaction strength was found to
be a function of the temperature ($T$) and applied magnetic field ($h$). The
scaling relation $R_c \sim h^{-\beta}f(Th^{\alpha})$, where,
$\alpha=0.23\pm0.01$ and $\beta = -0.06\pm0.01$, has been proposed, numerically
by the method of data collapse. The metastable volume fractions, for both
surface and bulk, were found to follow the Avrami's law. The critical relative
interaction strength ($R_c$) has been observed to decrease in an exponential
($e^{bL^{-1.5}})$ fashion with the system size ($L$).
