Pressure and temperature dependence of the Eu valence in EuNi2Ge2 and related systems studied by Mössbauer effect, X-ray absorption and X-ray diffraction☆

Abstract The effect of pressure and temperature on the valence state of Eu in EuNi 2 Ge 2 systems and the related systems EuNi 2 Si 2 , EuNi 2 Si 0.5 Ge 1.5 and EuPl 2 Ge 2 was studied by 151 Eu-Mossbauer spectroscopy, EuL III X-ray absorption and X-ray diffraction. Pressure-induced valence transitions from a divalent towards a trivalent state were observed in EuNi 2 Ge 2 around 5 GPa and in the quasi-ternary EuNi 2 Si 0.5 Ge 1.5 system around 0.5 GPa. In EuNi 2 Ge 2 we found from Mossbauer spectra measured at various pressures and temperatures a new type of valence transition, where an initially homogeneous valence state near to divalency segregates into two different valent states. From these data we derive for EuNi 2 Ge 2 the pressure and temperature dependence of the Eu valence and magnetism.