Effect of annealing temperature on magnetoresistivity, activation energy, irreversibility and upper critical field of the Cu-diffused MgB2 bulk superconductors
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Dosyalar
Tarih
2013
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Springer
Erişim Hakkı
info:eu-repo/semantics/closedAccess
Özet
This study manifests the change of the pinning mechanism, superconducting and physical properties of Cu-diffused MgB2 superconductors prepared at different annealing temperature from 650 to 850 degrees C by means of the magnetoresistivity measurements conducted at several applied magnetic fields in a range of 0-7 T as a function of temperature from 15 to 50 K. The onset (T-c(onset)) and offset (T-c(offset)) critical temperatures, activation energies (U-0), irreversibility fields (mu H-0(irr)), upper critical fields (mu H-0(c2)), residual resistivity ratios (R-R), cross-sectional area fractions (A(F)), penetration depths (lambda), coherence lengths (xi) and electronic mean free path (l) of the samples are evaluated from the magnetoresistivity curves. Thermally activated flux creep (TAFC) model is used for the determination of the U-0 values; likewise, the mu H-0(irr) and mu H-0(c2) values are obtained by resistivity criteria of 10 and 90 % normal-state resistivity, respectively. At absolute zero temperature (T = 0 K), the extrapolation of the mu H-0(irr)(T) and mu H-0(c2)(T) curves is used to find the mu H-0(irr)(0) and mu H-0(c2)(0) values of the samples. Moreover, the xi values are deduced from the mu H-0(c2)(0) values when the lambda values are calculated from the Ginzburg-Landau parameter (kappa). It is found that the superconducting and physical properties of the samples improve with the increment of the diffusion-annealing temperature; however, the presence of the magnetic field leading to the decrease of the flux pinning in the samples causes the reduction of these properties. Namely, the T-c(offset) and T-c(offset) values are found to increase from 38.4 to 39.3 K and 36.9 and 38.3 K with the enhancement in the diffusion-annealing temperature at zero filed. Similarly, the U-0 values increase significantly with the increase of the annealing temperature. In fact, the U-0 of 9,162 K belonging to the sample annealed at 850 degrees C is determined to be the maximum activation energy value. On the other hand, the minimum T-c(offset) of 30.9 K, T-c(offset) of 27.6 K and U-0 of 1,365 K at 7 T applied magnetic field are obtained for the pure sample, indicating that the sample annealed at 850 degrees C obtains much stronger flux pinning, better crystallinity and connectivity between grains compared to the other samples prepared. Based on these results, the superconducting and physical properties of the MgB2 superconductors produced in this work are observed to enhance with the increase of the diffusion-annealing temperature as a result of the improvement of pinning abilities, crystallinity and connectivity between grains. The magnetic field and temperature dependence of the activation energy are also discussed.
Açıklama
Anahtar Kelimeler
Kaynak
Journal Of Materials Science-Materials In Electronics
WoS Q Değeri
Q1
Scopus Q Değeri
Q2
Cilt
24
Sayı
1
