  In addition to its promising potential for applications, GaV4S8 shows very
interesting physical properties with temperature and magnetic field. These
properties can be tuned by applying hydrostatic pressure in order to reveal and
understand the physics of these materials. Not only pressure induces an
insulator-to-metal transition in GaV4S8 but it also has an interesting effect
on the structural and magnetic transitions. Using a combination of AC
calorimetry, capacitance, and resistivity measurements under pressure, we
determine the evolution of the structural and magnetic transitions with
pressure and thus establish the T-P phase diagram of GaV4S8. To detect the
insulator-to-metal transition, we use optical conductivity and DC resistivity
measurements and we follow the evolution of the Mott gap under pressure. The
structural transition temperature increases with pressure and a second
transition appears above 6 GPa indicating a possible new phase with a very
small gap. Pressure has surprisingly a very weak effect on the ferromagnetic
transition that persists even very close to the IMT that occurs at around 14
GPa, implying that the metallic state may also be magnetic.
