Magnetic properties of RE _x Mo₆Se₈ compounds between 0.7 and 295 K

Abstract

Magnetization measurements are reported for seven members of the series of compounds RE _x Mo ₆ Se ₈ (x≈1; RE=La, Ce, Pr, Eu, Gd, Yb, and Lu). These measurements establish that Ce, Pr, and Gd ions are trivalent in these compounds, but that Eu and Yb are primarily divalent, in agreement with crystallographic data. Large deviations of the susceptibilities for CeMo ₆ Se ₈ , PrMo ₆ Se ₈ , and YbMo ₆ Se ₈ from Curie-Weiss behavior above 10 K are attributed predominantly to crystal field effects, and quantitative agreement between crystal field theory and the experimental data was obtained for CeMo ₆ Se ₈ above 25 K. Further, we find for Gd _1.2 Mo ₆ Se ₈ an unusually small spin exchange interaction between the Gd ions and conduction electrons, consistent with previous estimates of this quantity based on superconductivity data. For the Gd, Eu, and Ce compounds, the low-temperature data indicate very small Curie-Weiss temperatures of −1.7, −0.6, and +0.4 K, respectively. No evidence for magnetic ordering of the RE ions in any of the above compounds was observed, with the exception of CeMo ₆ Se ₈ , for which the magnetization data at 0.7–1.3 K suggest the onset of ferromagnetic order.