Mössbauer effect in YbBe13: Mixed valence and magnetic ordering

Mössbauer effect investigations on the cubic intermetallic compound YbBe₁₃ in the temperature range between 0.065 K and 81 K are reported. Above the magnetic ordering temperatureT _Neel=1.27 K the results cannot be explained by a Γ₇ groundstate of Yb³⁺. There is evidence for the Yb ion being in a mixed valent state and the degree of hybridisasation being dependent on the magnetic ordering. Below the magnetic ordering temperature a Γ₇ groundstate of a 3⁺ Yb ion is found.