Evidence for Magnetic Ordering in the Heavy-Electron Compound CeCu₂In

Specific-heat and Cu NMR measurements have been made on the recently discovered heavy-electron compound CeCu₂In. The low-temperature specific heat has an enormous electronic contribution with C_e1/T ⋍ 1.2 J/mole·K² below 1.2 K, and shows a broad maximum at around 2.2 K. Below 2.3 K, Cu NMR linewidth ΔH shows appreciable additional broadening, and the nuclear transverse relaxation also becomes appreciably slower. These results indicate that CeCu₂In undergoes an antiferromagnetic phase transition at T_N ⋍ 2.3 K. The possibility of ordering of quite a small moment is suggested from the observations of the gigantic value of C_e1/T below T_N, the small magnetic entropy at T_N, and the steady increase of C_e1/T through T_N with decreasing temperature.