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EuB6 is Calcium hexaboride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Eu is bonded in a 1-coordinate geometry to twenty-four equivalent B atoms. All Eu–B bond lengths are 3.07 Å. B is bonded in a 1-coordinate geometry to four equivalent Eu and five equivalent B atoms. There is one shorter (1.68 Å) and four longer (1.76 Å) B–B bond length.
Despite the simplicity of their cubic crystal lattice, rare-earth hexaborides display complex physical properties including a (long debated) onset of metallization via magnetic polaron formation at T c1 approximate to 15 K preceding ferromagnetic ordering at T c2 approximate to 12 K. Here, in this work, we used applied pressure to tune the interplay between electronic structure and magnetism in EuB6. We probed the magnetism, valence, and structure of EuB 6 under quasi-hydrostatic pressures up to 30 GPa using X-ray techniques. Our findings show evidence for collapse of ferromagnetism above 20 GPa following a monotonic increase of mean Eu valence. While X-ray diffraction measurements in the paramagnetic state at room temperature show that the lattice retains cubic symmetry, a measurable quadrupole interaction seen by time-domain synchrotron Mössbauer spectroscopy suggests a lowering of symmetry associated with magnetic ordering, becoming more prominent across the magnetic transition. The interplay between conduction band electron count and magnetism observed under applied pressure in EuB 6 opens possibilities for fine-tuning metallization and magnetic properties of similar Eu-based semi-metal systems.