Magnetic moments and Pu form factor inPuFe2

Neutron diffraction experiments using both polarized and unpolarized beams have been performed on a small (40 mg) single crystal of ${}_{}{}^{239}{}_{}{}^{}\mathrm{PuFe}_2^{}{}_{}{}^{}$. This material has the cubic Laves phase structure and is ferromagnetic at ∼560 K. The polarized-neutron experiments have shown that (a) the easy direction for both the Pu and Fe moments is 〈100〉, (b) the moments are (0.39±0.02)${\mu }_B$ and (1.73±0.01)${\mu }_B$ for the Pu and Fe atoms, respectively, (c) the Fe form factor is the same as in iron metal, and (d) the form factor of Pu is very unusual. The Pu form factor is very different from that found recently in PuSb and cannot be analyzed with a straightforward crystal-field ground state. We suggest that hybridization effects, presumably in the main part between the 3d iron and 5f plutonium electrons, play a significant role in modifying the spin and orbital contributions that give rise to the unusual Pu form factor.