D. K. Finnemore

Specific-heat jump at Tc for Nd sub 1. 85 Ce sub 0. 15 CuO sub 4 minus y

The superconducting free-energy surface of grain-aligned Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}{ital y}} was measured to determine whether these electron-carrier materials have thermodynamic variables similar to the other high-temperature superconductors. There is a wide area in the {ital H}-{ital T} plane near {ital T}{sub {ital c}}, where the magnetization is reversible, just as was found for the Y, Bi, and Tl cuprates. The magnetic-field dependence of the specific heat derived from these data, {ital C}{sub 0}{minus}{ital C}{sub {ital H}}, shows a peak in the fluctuation region near {Tc} of about 1.2 mJ/cm{sup 3} K for {ital H}=2 T and {bold H}{parallel}{bold c}. At lower temperatures, below 16 K, the magnetically derived specific heat is nearly independent of field just as was found for the other high-{Tc} materials. A study of the transformation from the reversible to the irreversible regime using flux-creep and critical-current studies shows that the pinning potential to thermal energy ratio, {ital U}{sub eff}/{ital kT}, gradually rises from 2 to 20 at roughly the same value of reduced temperature, {ital T}/{ital T}{sub {ital c}}, as the Bi and Tl compounds.

Specific-heat jump at T c for Nd 1.85 Ce 0.15 CuO 4 − y

The superconducting free-energy surface of grain-aligned Nd{sub 1.85}Ce{sub 0.15}CuO{sub 4{minus}{ital y}} was measured to determine whether these electron-carrier materials have thermodynamic variables similar to the other high-temperature superconductors. There is a wide area in the {ital H}-{ital T} plane near {ital T}{sub {ital c}}, where the magnetization is reversible, just as was found for the Y, Bi, and Tl cuprates. The magnetic-field dependence of the specific heat derived from these data, {ital C}{sub 0}{minus}{ital C}{sub {ital H}}, shows a peak in the fluctuation region near {Tc} of about 1.2 mJ/cm{sup 3} K for {ital H}=2 T and {bold H}{parallel}{bold c}. At lower temperatures, below 16 K, the magnetically derived specific heat is nearly independent of field just as was found for the other high-{Tc} materials. A study of the transformation from the reversible to the irreversible regime using flux-creep and critical-current studies shows that the pinning potential to thermal energy ratio, {ital U}{sub eff}/{ital kT}, gradually rises from 2 to 20 at roughly the same value of reduced temperature, {ital T}/{ital T}{sub {ital c}}, as the Bi and Tl compounds.