Investigation of the second transition in U1xThxBe13

J. S. Kim, B. Andraka, and G. R. Stewart
Phys. Rev. B 44, 6921 – Published 1 October 1991
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Abstract

We have prepared extremely high-purity samples of U0.97Th0.03Be13 and U0.962Th0.038Be13 and conducted a study of the specific heat in zero field on the as-prepared and annealed samples. In addition we have measured the low-temperature specific heat of the 3 at. % Th sample in 0.25, 0.5, 0.75, 1.0, 1.25, 2, and 3 T magnetic fields in order to accurately determine Hc2 for both transitions. The high-purity unannealed 3.8 at. % Th samples show larger and sharper transitions than previously reported; annealing further improves the transitions such that ΔC(Tc2) for the 3 at. % Th sample is more than twice as large as previously reported, with Tc2 being approximately the same. A γ value of 2300 mJ/mol K2 for U0.97Th0.03Be13 is derived from entropy considerations and the 0-field and 3-T specific-heat data. The separation between the two transitions is significantly improved with annealing—ΔC(Tc1), which is essentially only a shoulder on ΔC(Tc2) for unannealed 3.8 at. % Th samples, becomes a clearly distinct transition upon annealing. The results of the field measurements are that the Hc2(T) data for the two transitions are, within our (rather good) precision, parallel; this includes the data as H→0, i.e., Hc2(Tc) for the two transitions is the same, ≈-45±3 T/K. This result is consistent with the Hc2 value reported for pure UBe13 suppresses. These field results contradict the two previous specific-heat-in-field studies (on unannealed lower-purity samples with significantly more scatter in the Hc2 data) of the two transitions in U1xThxBe13. The equality of Hc2(Tc1), Hc2(Tc2), and Hc2 for pure UBe13 demonstrated here is difficult to explain on the basis of current theories that consider the lower transition as a magnetic superconducting state.

  • Received 18 March 1991

DOI:https://doi.org/10.1103/PhysRevB.44.6921

©1991 American Physical Society

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Vol. 44, Iss. 13 — 1 October 1991

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