Magnetic form factor of 5f electrons in PuSb

The magnetic form factor of the 5f electrons around the Pu nucleus has been measured with neutrons. The experiment used polarized neutrons and a single crystal of weight 55 mg of PuSb. This compound, which has the NaCl crystal structure, is ferromagnetic below 67 K. The experiment was done in the ordered state with an applied field of 46 kOe. The results show that the Pu ion is trivalent; we see the maximum in f(Q) at Qapprox. =2.5 A-1, which is the unambiguous signature of the 5f5 state. A detailed analysis shows that the ground-state wave function is close to that of a GAMMA8 state in intermediate coupling. The analysis makes use of the large azimuthal anisotropy (variation in magnetic scattering depending on the angle the scattering vector makes with the magnetic moment) and is not consistent with any possible GAMMA7 state