The neutron elastic magnetic cross section has been measured from ferromagnetic ${}_{}{}^{242}{}_{}{}^{}\mathrm{PuP}$ at 4.2 K. As a result of the partial cancellation of $\overrightarrow{\mathrm{S}}$ and $\overrightarrow{\mathrm{L}}$ in the $f^5$ state, the cross section is independent of angle for $\frac{sin\theta }{\lambda }<0.35\mathrm{}$ ${\mathrm{\AA }}^{-1\mathrm{}}$. A detailed analysis, including the effects of intermediate coupling and $J$ mixing, allows an identification of the electronic ground state. The conduction-electron polarization ($\sim 0.35{\mu }_B$) is antiparallel to, and almost half the magnitude of, the localized $5f$ moment ($0.77{\mu }_B$).

• Received 24 June 1976

DOI:https://doi.org/10.1103/PhysRevB.14.4064