Heat capacity and magnetic properties of pyrochlore Hg 2Os 2O 7

Abstract

Hg 2Os 2O 7, which has the cubic pyrochlore structure, remains metallic down to the liquid helium temperature unlike its isostructural counterpart Cd 2Os 2O 7, which shows metal–insulator transition at 226 K. Magnetization and heat capacity data for Hg 2Os 2O 7 are presented. The magnetic anomaly at T N=88 K shares many characteristics in common with the metal–insulator transition in Cd 2Os 2O 7, though Hg 2Os 2O 7 remains metallic below T N. The heat capacity C p shows no or very little change in the magnetic entropy around T N, supporting the view that there is no long-range ordering of localized spins. The measured value of electronic heat-capacity coefficient γ=21 mJ K −2mol −1 is comparable to the value obtained from band-structure calculation on Cd 2Os 2O 7, suggesting that mass-enhancement is small in Hg 2Os 2O 7. There is a pronounced peak in C p/ T 3 at 13.1 K, which corresponds to a peak in the phonon density of states at 40 cm −1.