Evidence of ferromagnetism collapse and valence instability in the EuB$_6$ at high pressures

Rare earth hexaborides compounds have attracted research interest over the last few decades due to their rich and complex phase diagram besides their simple crystal structure, what gives to this family a wide spectrum of potential applications and make them ideal prototypical materials to explores new physical phenomena. Despite the fact that a majority of related research focuses on the topological insulator candidate SmB$_6$, recently proposals of a non-trivial band topology in parent compounds YbB$_6$ and EuB$_6$ are provoking strong interest especially due to the possibility for tuning hexaborides structural and electronic parameters to induce new topological phases. EuB$_6$ is the unique rare earth hexaboride that orders ferromagnetically going through two phase transitions and also presenting magnetic polarons formation. Here, by combining X-ray absorption and synchrotron Mossbauer spectroscopy we find that applying pressures higher than 20 GPa dramatically suppresses magnetic ordering in the material and induces an increase on its main valence, shifting it from a pure divalent state to a state with 2.2 mean valence at 28 GPa. The observed tunable electronic and magnetic phases in EuB$_6$ may provide important insight into interplay between structural, magnetic and electronic degrees of freedom in correlated electron material and topological physics.