  The quasi-one-dimensional antiferromagnetic Ising-like compound BaCo2V2O8 has
been shown to be describable by the Tomonaga-Luttinger liquid theory in its
gapless phase induced by a magnetic field applied along the Ising axis. Above
3.9 T, this leads to an exotic field-induced low-temperature magnetic order,
made of a longitudinal incommensurate spin-density wave, stabilized by weak
interchain interactions. By single-crystal neutron diffraction we explore the
destabilization of this phase at a higher magnetic field. We evidence a
transition at around 8.5 T towards a more conventional magnetic structure with
antiferromagnetic components in the plane perpendicular to the magnetic field.
The phase diagram boundaries and the nature of this second field-induced phase
are discussed with respect to previous results obtained by means of nuclear
magnetic resonance and electron spin resonance, and in the framework of the
simple model based on the Tomonaga-Luttinger liquid theory, which obviously has
to be refined in this complex system.
