Transport anomalies and magnetic properties of Sn x Eu1.2?x Mo6S8 alloys

Abstract

We have measured the resistance R, magnetoresistance, and magnetization of sintered samples of the compounds Sn x Eu1.2−x Mo6S8, where x = 0, 0.12, 0.24, and 0.48. A large resistance anomaly beginning at T ~ 100 K and extending to low temperatures is found in all of the alloys except x = 0.48, which had a high superconducting transition temperature T c ~ 11.3 K. The resistance anomaly, which appears to be correlated with the depression of T c, is also correlated with a large negative magnetoresistance at temperatures T ⩽ 12 K. For all samples except x = 0.48, that part of the magnetoresistance attributed to spin-flip scattering is proportional to the square of the magnetization M 2 and is 30–40% of R (0) for some samples. Magnetization measurements are consistent with a spin-7/2 paramagnetic behavior of Eu2+ ions when allowance is made for a concentration of 20–30% nonmagnetic (J = 0) Eu3+ ions as determined from Mossbauer measurements. The experimental results are inconsistent with predictions of dilute magnetic alloy Kondo models. We speculate that the resistance anomaly and suppression of T c for x ⩽ 0.24 are associated with a semiconductor-like behavior.