Magnetism of europium under extreme pressures

Abstract

Using synchrotron-based M\"ossbauer and x-ray emission spectroscopies, we explore the evolution of magnetism in elemental (divalent) europium as it gives way to superconductivity at extreme pressures. Magnetic order in Eu is observed to collapse just above 80 GPa as superconductivity emerges, even though Eu cations retain their strong local $4{f}^{7}$ magnetic moments up to 119 GPa with no evidence for an increase in valence. We speculate that superconductivity in Eu may be unconventional and have its origin in magnetic fluctuations, as has been suggested for high-${T}_{\mathrm{c}}$ cuprates, heavy fermions, and iron-pnictides.