ELECTRONIC-STRUCTURE PROPERTIES OF NEPTUNIUM INTERMETALLICS UNDER PRESSURE FROM MOSSBAUER-SPECTROSCOPY

Electronic structure properties of neptunium intermetallics obtained b y the 60 keV Mossbauer resonance in Np-237 in the pressure range up to 9 GPa and at temperatures from 1.5 K to about 150 K together with X-r ay determinations of the bulk modulus are discussed. Samples of the Na Cl compounds NpX, the Laves phases NpX(2) and the AuCu3 materials NpX( 3) as well as the tetragonal series NpX(2)Si(2) have been studied. The volume coefficients of magnetic moment and magnetic transition temper ature allow the classification in terms of 5f bandwidth arising either from 5f-5f overlap or hybridization with ligand s, p, or d electrons. The pressure-temperature magnetic phase diagram of some of these comp ounds has also been investigated. In NpGa3 and NpIn3 we find a prefere nce for ferromagnetic order under reduced volume. Finally we address t he question of crystal field interactions and show that even in a some what delocalized case (NpAl2) they are decisive in determining the hig h pressure Mossbauer spectra.