Agradecimentos: We acknowledge Flavio Gandra, Michael Nicklas and Cristoph Geibel for fruitful discussions. We thank the financial support from the Brazilian agencies CNPq, CAPES and FAPESP, Brazil (Grants 2018/00823-0, 2018/19015-1, 2021/02314-9 and 2022/05447-2). RDdR and L.O.K acknowledges financial support from the Max Planck Society, Germany under the auspices of the Max Planck Partner Group R. D. dos Reis of the MPI for Chemical Physics of Solids, Dresden, Germany. L.F. acknowledge financial support from FAPESP grant 2018/10585-0. E.H.T.P and G.A.L acknowledge financial support from CNPq studentship grant No. 136119/2018-2 and No. 140632/2018-2 respectively. We are grateful to GSECars for the help with gas loading in SMS experiments. Work at Argonne is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC-02- 06CH11357. Work at Los Alamos National Laboratory was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering. This research used facilities of the Brazilian Synchrotron Light Laboratory (LNLS), part of the Brazilian Center for Research in Energy and Materials (CNPEM), a private non-profit organization under the supervision of the Brazilian Ministry for Science, Technology, and Innovations (MCTI). The EMA beamline and LCTE staff are acknowledged for the assistance during the experiments 20210101. W.B. acknowledge support from the support from National Science Foundation (NSF), USA CAREER Award No. DMR-2045760 Ver menos

Abstract: 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 Tc1 approximate to 15 K preceding ferromagnetic ordering at Tc2 approximate to 12 K. 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 EuB6 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 M & ouml;ssbauer 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 EuB6 opens possibilities for fine-tuning metallization and magnetic properties of similar Eu-based semi-metal systems Ver menos