We review experimental studies of the time decay of the nonequilibrium magnetization in high-temperature superconductors, a phenomenon known as magnetic relaxation. This effect has its origin in motion of flux lines out of their pinning sites due to thermal activation or quantum tunneling. The combination of relatively weak flux pinning and high temperatures leads to rich properties that are unconventional in the context of low temperature superconductivity and that have been the subject to intense studies. The results are assessed from a purely experimental perspective and discussed in the context of present phenomenological theories. [S0034-6861(96)00403-5]

Magnetic relaxation in high-temperature superconductors

Review of stability in high temperature superconductors with emphasis on flux jumping

Local magnetic relaxation in high-temperature superconductors.

The effective activation energy Ue(T,H) in epitaxial GdBa2Cu3O7−δ thin films

Thermally activated flux flow and vortex glass transition of the recently discovered SmFeAsO0.9F0.1 superconductor are studied in magnetic fields up to 9.0 T. The thermally activated energy is analyzed in two analytic methods, of which one is conventional and generally used, while the other is closer to the theoretical description. The thermally activated energy values determined from both methods are discussed and compared. In addition, several critical magnetic fields determined from resistivity measurements are presented and discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/22/6/065012/pdf

Thermally activated energy and critical magnetic fields of SmFeAsO0.9F0.1

The broadening of the resistive transition in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ epitaxial thin film was measured in various applied magnetic fields. The irreversibility line and its angular dependence were obtained. The temperature and magnetic field dependence of the activation energy ${U}_{0}(H,T)\ensuremath{\propto}{U}_{0}[1\ensuremath{-}{T/T}_{c}(0)]{(H}_{0}/{\ensuremath{\varepsilon}}_{\ensuremath{\theta}}{H)}^{2/3}$ were obtained from the experimental results, which is consistent with the expression of the activation energy for thermally excited flux creep deduced from the irreversibility line and Arrhenius law except for low field data in which the prefactor of the Arrhenius law has little deviation from that in high fields.

Dependence of activation energy upon magnetic field and temperature in YBa 2 Cu 3 O 7-δ epitaxial thin film

This paper is based on the systematic research of specialized parameters of the concentration of fluorine doping and heat treatment for high-Tc (Bi1.6Pb0.4)Sr2Ca2Cu3Oy-xFx superconductors (x=0.00, 0.20, 0.40, 0.64, 0.74, 0.84) synthesized by solid state reaction methods. The zero-resistence temperatures Tc are raised more than 10 K, the highest Tc being 116–118 K. The critical current density Jc, magnetic hysteresis 4πM, and flux-pinning potential U0 are greatly increased. The relationships between flux-creep velocity S and external magnetic field H, U0 and H, Jc and H, and irreversible magnetic field H∗ and T are obtained. The pinning effect of F for the superconductor is discussed.

Studies of superconductivity in 118 K high-Tc (Bi,Pb)SrCaCuO-F superconductors

The magnetization behaviors of single phase Y1Ba2Cu3O7−δ bulk superconductors have been studied by measurement of the DC susceptibility. It is found that there are two lower critical field. One which is near 10 Oe at 77K is defined as a weak lower critical field and denoted by HclJ. dHc1J/dT is about 0.2 Oe/K near Tc. Another is still called as usual lower critical field, Hcl. It is 60 Oe at 77K and dHc1/dT is about 4.6 Oe/K. The detailed measurement of DC magnetization shows also that an anomaly of the magnetization curve appears between HclJ and Hc1. The amplitudes of anomalous peak and valley have some difference depending on how samples are prepared. The mechanism of Hc1J appearance and the anomaly of the magnetization has been discussed in “Soft Sponge Model” which will be published in Chin. J. Low Temperature Physics.

Cao Xiao-Wen

Papers

Dependence of activation energy upon magnetic field and temperature in YBa 2 Cu 3 O 7-δ epitaxial thin film

Studies of superconductivity in 118 K high-Tc (Bi,Pb)SrCaCuO-F superconductors

A NEW LOWER CRITICAL FIELD AND ANOMALY OF MAGNETIZATION CURVE IN HIGH TcY1Ba2Cu3O7−δ BULK SUPERCONDUCTORS

The single phase Y1Ba2Cu3O7−δ bulk is a weak pinning superconductor

A high Tc proximity effect superconductor and its superconductivity