  Neutron stars with very strong surface magnetic fields have been suggested as
the site for the origin of observed soft gamma repeaters (SGRs). In this paper
we investigate the influence of such strong magnetic fields on the properties
and internal structure of these magnetized neutron stars (magnetars). We study
properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas
with and without the effects of the anomalous nucleon magnetic moments in a
magnetic field. The presence of a sufficiently strong magnetic field changes
the ratio of protons to neutrons as well as the neutron drip density. We also
study the appearance of muons as well as pion condensation in strong magnetic
fields. We discuss the possibility that boson condensation in the interior of
magnetars might be a source of SGRs.
