High-Pressure Studies of Valence and Magnetic State in Europium Metal

The strong local-moment magnetism in divalent Eu metal (4f$^{7}$) suppresses superconductivity. At extreme pressure Eu is expected to become trivalent and nonmagnetic (4f$^{6}$). Recently, superconductivity in Eu was discovered by Debessai \textit{et al}. for pressures above 80 GPa [1]. However, Eu's transition temperature lies near 2 K, nearly an order of magnitude lower than for comparable trivalent d-electron metals, possibly because Eu is not fully trivalent but rather mixed valent. Here we report recent experimental results on Eu's valence and magnetic state to Mbar pressures through synchrotron x-ray absorption near edge structure (XANES), synchrotron x-ray magnetic circular dichroism (XMCD), and synchrotron M\"{o}ssbauer spectroscopy (SMS).\\[4pt] [1] M. Debessai, T. Matsuoka, J. J. Hamlin, J. S. Schilling, and K. Shimizu, Phys. Rev. Lett. 102, 197002 (2009).