Free-energy surfaces for superconductingY1Ba2

Abstract

Magnetization studies were undertaken to determine the change in free energy of the superconducting state of YiBa2Cu307 with changes in magnetic field and temperature. Close to the transition temperature T, magnetic Aux moves easily and reversibly in these materials so that magnetization is a thermodynamically reversible variable. Hence, the free-energy surfaces can be measured and quantities such as entropy and specific heat can be derived. Magnetization is found to be linear in (T, -T)~n ear T,. The free-energy surface shows substantial changes with magnetic field all the way up to 92 K, well outside the usual 0,2 vs T plots derived from resistivity or ac susceptibility data.

Magnetic flux motion and flux pinning in superconductors

“…4.7 respectively. Free-energy curves for NCCO are qualitatively similar to the curves obtained for Tl(2212) and Tl(2223) [Fang et al, 1989], and Y123 [Athreya et al, 1988;Gohng and Finnemore, 1990] in that they exhibit curvature near Tc, but almost no curvature several degrees below Tc (about 17K in this case). .100-1 1 , , The field dependence of the specific heat jump, Q-CH, is related to the curvature in GH-GO by Eqn.…”

Thermodynamic properties

“…The transition is first order so that the change in G at T 0 c is continuous, but the change in its derivative is discontinuous (cf. Athreya et al, 1988). (Athreya et al, 1988). applied field close to the superconducting transition temperature.…”

“…Athreya et al, 1988). (Athreya et al, 1988). applied field close to the superconducting transition temperature. The free-energy differences are obtained by integrating Eq.…”

“…23 Magnetic field dependence of the specific heat difference for parallel and perpendicular fields(Athreya et al, 1988).B ⊥ (a.b)…”

Magnetic properties of high-T[subscript c] superconductors

“…The change in free energy G(H) with magnetic field H can be calculated by integrating equilibrium magnetization M over H [Athreya et al, 1988). Since free energy is one of the fundamental thermodynamic quantities as well as one of a few parameters that directly relates magnetic properties of a superconductor with thermodynamic properties, it is of interest to construct the free-energy surface over H-T plane for both melt-textured Eind grain-aligned YBCO samples and compeire them.…”