  The ferromagnetic phase in pure neutron matter as well as charge neutral,
beta-equilibrated nuclear matter is considered. We employ Quantum
Hadrodynamics, a relativistic field theory description of nuclear matter with
meson degrees of freedom, and include couplings between the baryon (proton and
neutron) magnetic dipole moment as well as between their charge and the
magnetic field in the Lagrangian density describing such a system. We vary the
strength of the baryon magnetic dipole moment till a non-zero value of the
magnetic field, for which the total energy density of the magnetised system is
at a minimum, is found. The system is then assumed to be in the ferromagnetic
state.
  The ferromagnetic equation of state is employed to study matter in the
neutron star interior. We find that as the density increases the ferromagnetic
field does not increase continuously, but exhibit sudden rapid increases. These
sudden increases in the magnetic field correspond to shifts between different
configurations of the charged particle's Landau levels and can have significant
observational consequences for neutron stars. We also found that although the
ferromagnetic phase softens the neutron star equation of state it does not
significantly alter the star's mass-radius relationship.
  The properties of magnetised symmetric nuclear matter were also studied. We
confirm that magnetised matter tends to be more proton-rich but become more
weakly bound for stronger magnetic fields. We show that the behaviour of the
compressibility of nuclear matter is influenced by the Landau quantisation and
tends to have an oscillatory character as it increases with the magnetic field.
The symmetry energy also exhibits similar behaviour.
