  The chemical evolution of nascent quark matter core in a newborn compact
neutron star is studied in presence of a strong magnetic field. The effective
rate of strange quark production in degenerate quark matter core in presence of
strong magnetic fields is obtained. The investigations show that in presence of
strong magnetic fields a quark matter core becomes energetically unstable and
hence a deconfinement transition to quark matter at the centre of a compact
neutron star under such circumstances is not possible. The critical strength of
magnetic field at the central core to make the system energetically unstable
with respect to dense nuclear matter is found to be $\sim 4.4\times 10^{13}$G.
This is the typical strength at which the Landau levels for electrons are
populated. The other possible phase transitions at such high density and ultra
strong magnetic field environment are discussed.
