Strong crystalline electric fields and the magnetic and nuclear-magnetic-resonance properties of the actinide monophosphides: NpP

Abstract

The results of magnetization and NMR measurements on neptunium monophosphide are reported. NpP orders in a complex manner at 120°K, and the paramagnetic susceptibility departs from Curie-Weiss behavior. The Knight shift of ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ follows a Curie-Weiss law and ($T_{1}T$) is linear in temperature from 175-360°K. The results on NpP, as well as earlier results on UP and PuP, are discussed in terms of a nonperturbative treatment of the crystalline electric fields and the coupling of the conduction electrons to the localized moments on the actinides.