Volume dependence of f-electron structure in intermetallic compounds of Eu and Np from Mössbauer high pressure studies☆

Mossbauer spectroscopy on EuAl2 between 4.2 and 300 K at pressures up to 50 GPa coupled with X-ray diffraction studies in the same pressure range show — contrary to expectation — that this Laves phase material possesses a fully localized 4f7 configuration even under a volume reduction of ∼30%. The results on EuAl2 will briefly be compared to data on EuCu2Si2, a material exhibiting intermediate valence behavior. For a series of Np intermetallics it is shown that systematics of the volume coefficients ∂lnTmag−∂lnV and ∂lnμ−∂lnV (where Tmag = magnetic ordering temperature and μ = ordered momemt on Np) allows the distinction between compounds having a localized, a narrow band or a wide band 5f-electron structure.