Pressure-induced Yb valence transition and magnetism in YbMn6Ge6−xSnx

Abstract

We investigate the external pressure dependence of the crystal structure, Yb valence, and local magnetization in ${\mathrm{YbMn}}_{6}{\mathrm{Ge}}_{6\ensuremath{-}x}{\mathrm{Sn}}_{x}$ using x-ray diffraction, x-ray absorption near edge spectroscopy (XANES), and x-ray magnetic circular dichroism (XMCD). The application of physical pressure results in a weakly anisotropic unit cell volume contraction without modifying the crystal structure. The external pressure allows crossing the Yb magnetic instability, which occurs for strongly hybridized Yb (valence $\ensuremath{\approx}2.76$), with a concomitant slope change in the valence-pressure curve. In the Ge-rich compounds, Yb local magnetism vanishes at very high pressure ($P \ensuremath{\ge}39.8$ GPa) likely because of the simultaneous collapse of the Mn magnetism. The results underline similarities between external and chemical pressure increase, which favors trivalent and magnetic Yb. Some differences are observed in the Sn-rich compounds highlighting potential local pressure and/or electronic effects.