Hyperfine Interactions and Relaxation Effects in Laves-Phase Intermetallic Compounds of Neptunium

Abstract
Studies of magnetic properties of cubic Laves-phase compounds of Np have been performed using the Mössbauer effect of the 59.5-keV transition in Np237. The compounds studied were NpAl2, NpCo2, NpNi2, NpFe2, and NpIr2. Hyperfine-interaction parameters and ordering temperatures were deduced from these measurements. If the values of H(T)H(0) are plotted as a function of TTC, the points (except those of NpFe2) lie on the molecular-field-theory curve for S=12 Quadrupole interactions were found to be very small. This behavior is consistent with the assumption that the ground crystalline state in these compounds is an isolated Kramers doublet. Relaxation phenomena were observed in the spectra. The spectra could be fitted by assuming relaxation effects within the Kramers doublet with a relaxation time of ∼ 4 × 1011 sec. Isomer shifts were measured and found to change regularly with the size of the unit cell.