  We study a holographic model realizing an "antiferromagnetic" phase in which
a global SU(2) symmetry representing spin is broken down to a U(1) by the
presence of a finite electric charge density. This involves the condensation of
a neutral scalar field in a charged AdS black hole. We observe that the phase
transition for both neutral and charged (as in the standard holographic
superconductor) order parameters can be driven to zero temperature by a tuning
of the UV conformal dimension of the order parameter, resulting in a quantum
phase transition of the Berezinskii-Kosterlitz-Thouless type. We also
characterize the antiferromagnetic phase and an externally forced ferromagnetic
phase by showing that they contain the expected spin waves with linear and
quadratic dispersions respectively.
