I127Nuclear Quadrupole Resonance in Antiferromagnetic UI3

The ${\mathrm{I}}^{127}$ nuclear quadrupole resonance (NQR) spectrum in antiferromagnetic U${\mathrm{I}}_3$ was studied in the temperature range 1.4 to 2.4°K in zero external field in a polycrystalline sample. A total of 32 lines were observed in the frequency range 6 to 156 MHz. A computer analysis of the spectrum showed that there were three different magnitudes of local magnetic fields at the iodine sites: 14.08, 17.33, and 17.44 kG. These three field magnitudes were assigned to specific iodine sites in the U${\mathrm{I}}_3$ crystal, and the directions were determined to within an eightfold ambiguity by analogy with single-crystal NQR results for the isomorphic compound Nd${\mathrm{Br}}_3$. From these results the magnetic space group $P_c{2}_1{2}_{1}2$ is tentatively assigned. Analysis of the temperature dependence of the spectrum gives a sublattice magnetization curve which is unusually abrupt and is quite similar to that observed in U${\mathrm{O}}_2$.