  The large N_c N=4 gauge theory with quenched N=2 quark matter in the presence
of a magnetic field displays chiral symmetry breaking. We study the temperature
and chemical potential dependence of this theory using its gravity dual (based
on the D3/D7 brane system). With massless quarks, at zero chemical potential,
the theory displays a first order thermal transition where chiral symmetry is
restored and simultaneously the mesons of the theory melt. At zero temperature,
these transitions with chemical potential are second order and occur at
different chemical potential values. Between the three there are two
tri-critical points, the positions of which we identify. At finite quark mass
the second order transition for chiral symmetry becomes a cross over and there
is a critical point at the end of the first order transition, while the meson
melting transition remains similar to the massless quark case. We track the
movement of the critical points as the mass is raised relative to the magnetic
field.
