Mazet, T.Malterre, D.Francois, M.Dallera, C.Grioni, M.Monaco, G.2013-10-012013-10-012013-10-01201310.1103/PhysRevLett.111.096402https://infoscience.epfl.ch/handle/20.500.14299/95604WOS:000323715500007We investigate the temperature dependence of the Yb valence in YbMn6Ge1.8Sn4.2 and YbMn6Ge1.6Sn4.4 using resonant inelastic x-ray scattering experiments. Yb is found to be in an intermediate valent state in the whole investigated temperature range (10-450 K). We thus prove that the unusually high magnetic ordering temperature of Yb (similar to 60 and 90 K for x = 4.2 and 4.4, respectively) involves an intermediate valent Yb, an unprecedentedly observed phenomenon. Further, an anomalous increase in the Yb valence is observed upon cooling. A scenario is proposed to explain this unusual behavior. It is based on the presence of magnetically ordered Mn moments and on an Anderson Hamiltonian with a Zeeman term modeling the magnetic interactions.text::journal::journal article::research article