Nuclear ferromagnetic ordering of141Pr in the diluted Van Vleck paramagnets Pr1?x Y x Ni5

Abstract

We report on the first investigation of the effect of “magnetic dilution” on nuclear magnetic spin interactions in metals; we studied this effect in the diluted Van Vleck paramagnets Pr1−xYxNi5. In addition, we investigated the electronic magnetic properties of these intermetallic compounds. For this purpose, we have measured the nuclear and electronic susceptibilities of Pr1−xYxNi5 with x = 0 to 0.2 at 50μK ⩽ T ⩽8 mK and at 2.2 K ⩽ T ⩽ 300 K. We observe a linear decrease of the electronic Van Vleck susceptibility and of the hyperfine enhancement factor by 13% (per mole Pr3+). The hyperfine-enhanced nuclear susceptibility decreases by about a factor of three when going fromx = 0 tox = 0.2. The samples show nuclear ferromagnetic transitions of141Pr with nuclear Curie temperatures Tc decreasing from 370 μK to 100 μK and Weiss temperatures Θ decreasing from 218 μK to 13 μK in this concentration range. These data are compared with the results of mean-field calculations. In addition, we report on measurements of the nuclear spin relaxation time τ of these compounds, for which we find values of a few msec at millikelvin temperatures and a critical speeding-up at Tc. Our data give hints that for x > 0.2 the character of the nuclear magnetic transition may change, possibly to a nuclear spin glass freezing.