Relaxation of persistent current and the energy barrier Ueff(J) close to Tc in a grain-aligned YBa2Cu3O7-δ ring

I. Isaac, J. Jung, Masato Murakami, S. Tanaka, M. A K Mohamed, L. Friedrich

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Abstract

Abrikosov flux-creep-induced relaxation of persistent current was investigated close to Tc in a ring-shaped grain-aligned MPMG-processed YBa2Cu3O7-δ (with the c axis perpendicular to the ring's plane). The measurements were performed for a wide range of current (0<J<Jc), using zero-field-cooling procedure over a temperature range of 80-90 K. A scanning Hall probe system was used to measure profiles of the magnetic field (Hc) generated by the persistent current circulating in a ring. The magnitude of the current and its decay were inferred from the magnitude and decay of the magnetic field at the ring's center. Relaxation measurements were performed over a time scale between 30 s and 3×104 s. The results revealed two distinct relaxation regimes: (1) a steady-state logarithmic relaxation of the persistent current from an initial value J0 close to Jc and (2) a slow nonsteady nonlogarithmic initial relaxation at low values of J0, which eventually converges to a long-time steady-state logarithmic relaxation. The logarithmic decay of the persistent current is consistent with the Anderson flux-creep model. The slow nonlogarithmic initial relaxation of the persistent current for low values of J0 is due to a transient redistribution of magnetic flux over the sample volume, consistent with a theoretical analysis of nonlinear flux diffusion [Gurevich and Küpfer, Phys. Rev. B 48, 6477 (1993)]. At fixed value of time, Ueff(J) calculated from the Beasley, Labusch, and Webb [Phys. Rev. 181, 682 (1969)] rate equation for thermally activated motion of flux, is current independent up to about 0.6-0.7Jc and at higher currents it drops linearly with increasing current. Ueff(J,T) for a steady-state logarithmic relaxation provides a high-temperature extension of Ueff(J) measured at low temperatures in grain-aligned YBa2Cu3O7-δ with Maley's method [Phys. Rev. B 48, 13 992 (1993)], suggesting a gradual conversion of the flux-creep process from a vortex-glass or collective flux creep at low temperatures to Anderson single-barrier vortex creep at high temperatures.

Original languageEnglish
Pages (from-to)11806-11818
Number of pages13
JournalPhysical Review B
Volume51
Issue number17
DOIs
Publication statusPublished - 1995
Externally publishedYes

Fingerprint

Energy barriers
Fluxes
Creep
rings
energy
Vortex flow
Temperature
Magnetic fields
decay
Magnetic flux
vortices
barium copper yttrium oxide
Cooling
Scanning
magnetic fields
Glass
high current
magnetic flux
cooling
scanning

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Relaxation of persistent current and the energy barrier Ueff(J) close to Tc in a grain-aligned YBa2Cu3O7-δ ring. / Isaac, I.; Jung, J.; Murakami, Masato; Tanaka, S.; Mohamed, M. A K; Friedrich, L.

In: Physical Review B, Vol. 51, No. 17, 1995, p. 11806-11818.

Research output: Contribution to journalArticle

Isaac, I. ; Jung, J. ; Murakami, Masato ; Tanaka, S. ; Mohamed, M. A K ; Friedrich, L. / Relaxation of persistent current and the energy barrier Ueff(J) close to Tc in a grain-aligned YBa2Cu3O7-δ ring. In: Physical Review B. 1995 ; Vol. 51, No. 17. pp. 11806-11818.
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abstract = "Abrikosov flux-creep-induced relaxation of persistent current was investigated close to Tc in a ring-shaped grain-aligned MPMG-processed YBa2Cu3O7-δ (with the c axis perpendicular to the ring's plane). The measurements were performed for a wide range of current (0<J<Jc), using zero-field-cooling procedure over a temperature range of 80-90 K. A scanning Hall probe system was used to measure profiles of the magnetic field (Hc) generated by the persistent current circulating in a ring. The magnitude of the current and its decay were inferred from the magnitude and decay of the magnetic field at the ring's center. Relaxation measurements were performed over a time scale between 30 s and 3×104 s. The results revealed two distinct relaxation regimes: (1) a steady-state logarithmic relaxation of the persistent current from an initial value J0 close to Jc and (2) a slow nonsteady nonlogarithmic initial relaxation at low values of J0, which eventually converges to a long-time steady-state logarithmic relaxation. The logarithmic decay of the persistent current is consistent with the Anderson flux-creep model. The slow nonlogarithmic initial relaxation of the persistent current for low values of J0 is due to a transient redistribution of magnetic flux over the sample volume, consistent with a theoretical analysis of nonlinear flux diffusion [Gurevich and K{\"u}pfer, Phys. Rev. B 48, 6477 (1993)]. At fixed value of time, Ueff(J) calculated from the Beasley, Labusch, and Webb [Phys. Rev. 181, 682 (1969)] rate equation for thermally activated motion of flux, is current independent up to about 0.6-0.7Jc and at higher currents it drops linearly with increasing current. Ueff(J,T) for a steady-state logarithmic relaxation provides a high-temperature extension of Ueff(J) measured at low temperatures in grain-aligned YBa2Cu3O7-δ with Maley's method [Phys. Rev. B 48, 13 992 (1993)], suggesting a gradual conversion of the flux-creep process from a vortex-glass or collective flux creep at low temperatures to Anderson single-barrier vortex creep at high temperatures.",
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AU - Friedrich, L.

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