^{1,a)}, M. P. Chornomorets

^{1}, S. M. Ryabchenko

^{1}, E. A. Pashitskii

^{1}and A. V. Semenov

^{1}

### Abstract

The temperature dependence of the critical density of superconducting current [, and is the critical temperature] of two epitaxial-oriented thin filmsgrown on and substrates has been investigated by the method of dynamic magnetic susceptibility. In both samples, the dependence has two sections with power dependences and in the temperature region from to , with crossover between them. Measurements were made of the temperature dependences of the dynamic relaxation rate (magnetic flux creep), which turned out to be unconnected with the observed crossovers. It is shown that the observed features of are not caused, as was assumed earlier, by the limitation of the critical depairing current density in the interdislocation gaps of the interblock boundaries of epitaxialthin films. Based on numerical calculations, it is shown that the existence of crossovers and the breakdown of scaling detected in one of the samples ( is the dc magnetic field) in the magnetic-field dependences close to can be explained by the manifestation of macroscopic inhomogeneity of the samples in the local values of the critical temperature ( inhomogeneity). The absence of observable breakdown of the scaling in the second sample is explained by the smaller width of the distribution over in it by comparison with the first sample.

I. INTRODUCTION

II. EXPERIMENT

III. RESULTS

IV. DISCUSSION

CONCLUSION

### Key Topics

- Critical currents
- 48.0
- Rotating flows
- 34.0
- Magnetic fields
- 26.0
- Current density
- 19.0
- Magnetic films
- 16.0

## Figures

(a) Determining the critical temperature from the temperature dependence of the imaginary component of the magnetic susceptibility in a variable magnetic field . The straight line is a linear approximation of the high-temperature front of the dependence, and the arrows indicate the following: is the critical temperature, and is the temperature at the maximum . (b) The dependence of the values of (○) and (◻) on the amplitude of the measurement field, . Sample AC86.

(a) Determining the critical temperature from the temperature dependence of the imaginary component of the magnetic susceptibility in a variable magnetic field . The straight line is a linear approximation of the high-temperature front of the dependence, and the arrows indicate the following: is the critical temperature, and is the temperature at the maximum . (b) The dependence of the values of (○) and (◻) on the amplitude of the measurement field, . Sample AC86.

Temperature dependences (as a function of the reduced temperature ) of the measured critical current density (○) at frequencies of (a) and (b and c). The solid lines are approximations of the linear sections. The arrows indicate the ends of the linear sections ( and ) and the intersections of the linear approximations . The dashed line in (c) represents the results of calculations of the critical current density, taking into account the inhomogeneity. Sample PP8.

Temperature dependences (as a function of the reduced temperature ) of the measured critical current density (○) at frequencies of (a) and (b and c). The solid lines are approximations of the linear sections. The arrows indicate the ends of the linear sections ( and ) and the intersections of the linear approximations . The dashed line in (c) represents the results of calculations of the critical current density, taking into account the inhomogeneity. Sample PP8.

Temperature dependences (as a function of the reduced temperature ) of the measured critical current density (○) at frequencies of (a) and (b and c). The solid lines are approximations of the linear sections. The arrows indicate the ends of the linear sections ( and ) and the intersections of the linear approximations . The dashed line in (c) represents the results of calculations of the critical current density, taking into account the inhomogeneity. Sample AC86

Temperature dependences (as a function of the reduced temperature ) of the measured critical current density (○) at frequencies of (a) and (b and c). The solid lines are approximations of the linear sections. The arrows indicate the ends of the linear sections ( and ) and the intersections of the linear approximations . The dashed line in (c) represents the results of calculations of the critical current density, taking into account the inhomogeneity. Sample AC86

(a) Temperature dependences of the dynamic relaxation rate for samples PP8 (○) and AC86 (◻). The arrows correspond to the ends of the linear sections on the curves of Fig. 3 for the critical current density in sample AC86. (b) The data for sample AC86, shown as a function of . The solid line is an approximation of the experimental data by a dependence of the form .

(a) Temperature dependences of the dynamic relaxation rate for samples PP8 (○) and AC86 (◻). The arrows correspond to the ends of the linear sections on the curves of Fig. 3 for the critical current density in sample AC86. (b) The data for sample AC86, shown as a function of . The solid line is an approximation of the experimental data by a dependence of the form .

Dependences of the measured critical current density on parameters (a) and (b) at , K: 77 (◻), 83.5 (○), 84.5 (△), 85.5 (▽), and 86 (◇) for sample PP8. The values of the critical current density are normalized to the value . The experimental points are connected by curves for visibility.

Dependences of the measured critical current density on parameters (a) and (b) at , K: 77 (◻), 83.5 (○), 84.5 (△), 85.5 (▽), and 86 (◇) for sample PP8. The values of the critical current density are normalized to the value . The experimental points are connected by curves for visibility.

Temperature dependences of , determined at the following values of parameter , T: 0.2 (◻), 0.3 (○), and 0.5 (△). The solid curves are the results of calculations of the influence of inhomogeneity. Sample PP8.

Temperature dependences of , determined at the following values of parameter , T: 0.2 (◻), 0.3 (○), and 0.5 (△). The solid curves are the results of calculations of the influence of inhomogeneity. Sample PP8.

Magnetic-field dependences of the critical current density for sample AC86 at , K: 77.4 (◻), 80 (○), 82 (△), 84 (▽), and 86 (◇). (see Ref. 26, Fig. 6). The solid curve shows the approximation of the experimental data by the dependence obtained using the model proposed in Ref. 17.

Magnetic-field dependences of the critical current density for sample AC86 at , K: 77.4 (◻), 80 (○), 82 (△), 84 (▽), and 86 (◇). (see Ref. 26, Fig. 6). The solid curve shows the approximation of the experimental data by the dependence obtained using the model proposed in Ref. 17.

## Tables

Characteristics of the temperature dependences of the current density in Figs. 2 and 3. are the temperatures at the designated points, and and are the exponents on the linear sections and .

Characteristics of the temperature dependences of the current density in Figs. 2 and 3. are the temperatures at the designated points, and and are the exponents on the linear sections and .

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