A thermal-expansion study on the B-T phase diagrams of U1-xThxBe13 for 0≤x≤0.03

By means of high resolution dilatometry B-T phase diagrams of superconducting U1-xThxBe13 are explored for various x. Particular attention is paid to the lower of the subsequent phase transitions at T-c2 < T-c1 for x = 0.022 and 0.03. Our data provide strong evidence that for both concentrations T-c1(B) and T-c2(B) remain distinct for T greater than or equal to 0.15 K. By extending the experiments to subcritical Th concentrations x = 0.017 < x(er) approximate to 0.019, we find that the recently discovered anomaly at T-L(x) < T-c(x) shows a similar field dependence as the transition at T-c2, consistent with the suggestion that the anomaly at T-L marks the precursor of the transition at T-c2 (C) 1999 Elsevier Science B.V. All rights reserved.