A scaling law for ac susceptibility of an YBa2Cu3O film in a perpendicular ac field

Abstract

The ac susceptibility (ACS) of an YBa2Cu3O thin film in a perpendicular ac magnetic field (Ha) from 0.22 to 30.8 G is measured as a function of temperature. The temperature dependence of the real (χ′) and imaginary (χ′′) parts of the ACS for various Ha can be well scaled onto a single curve using the peak value (χp″) and temperature (Tp) of χ′′(T) as the scaling parameters. The scaling law suggests that the critical state can be established only below Tp. Above Tp, the ACS is determined by the screening effect of the film due to the sharp decrease of its resistance. Below Tp, the scaling behavior is in agreement with the theoretical approaches based on the critical state model, only if the temperature for zero critical current density is related to the irreversibility temperature Tirr rather than Tc. From the scaling law, we found that Tirr=Tp.

Alternating current susceptibility measurements of inter-grain critical current density in sintered Bi1.8Pb0.2Sr2Ca2Cu3Oy

“…The critical exponent β for J * c has been predicted to be unity for the Josephson tunnel junctions [30] and 3/2 for the micro-bridge junctions [31] by Ginzburg-Landau theory, while the values of β for high T c materials were determined for YBCO films by the χ ac measurements [12,[15][16][17] on the basis of the Bean critical state model. In these experiments, the external field was applied perpendicular to the film surface.…”

“…Recently, the experimental results of ac magnetic susceptibility χ ac have been discussed by the critical state models for the mixed state of type-II high T c superconductors [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In the critical state under the magnetic field between H c1 and H c2 , the force balance holds between the pinning force density f p and the Lorenz force density J B int .…”