Magnetic and Thermal Properties of UI3at Liquid Helium Temperatures

Previous measurements of the magnetic susceptibility of U${\mathrm{I}}_3$ revealed a susceptibility maximum near 3.2°K of antiferromagnetic character, and a second susceptibility maximum at 1.5°K which is strongly depressed by an applied magnetic field of only 5 to 10 oersteds. The specific heat of U${\mathrm{I}}_3$ has now been measured from 1.2° to 4.2°K. These measurements show a $\lambda$-type anomaly of magnitude 10 joules/mole-deg at 2.61°K which is interpreted as arising from the antiferromagnetic transition. The behavior of the entropy and specific heat curves indicates an extensive short-range order above the antiferromagnetic transition point. The lower temperature susceptibility anomaly is tentatively interpreted as a manifestation of the growth of long-range antiferromagnetic order.