Thermally-activated and temperature-independent magnetic relaxation in aligned grains of NdFeAsO(F)

ORAL

Abstract

We have studied flux creep in a magnetically-aligned powder of NdFeAsOF and found it to be strikingly similar to the situation in cuprates. The magnetic relaxation rate S=-dlnM$_{irr}$/dlnt is linear in temperature at low temperatures. There is an extrapolated~finite creep rate of about S=-0.02 at T=0, indicative of a quantum tunneling of vortices under energy barriers. This quantum creep rate is field-independent. From the temperature-dependent creep data we have obtained activation energy as a function of persistent current density, U(J). Comparison with existing creep theories will be made.

*Research sponsored by the DOE Division of Materials Sciences and Engineering

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Authors

  • J.R. Thompson

    • Dept. of Physics, University of Tennessee and Oak Ridge National Laboratory
    • Dept Physics, Univ. Tennessee, Knoxville, TN, USA
    • U. of Tennessee
    • Dept. of Physics, University of Tennessee, and Oak Ridge National Laboratory
    • University of Tennessee

  • Yuri L. Zuev

    • Oak Ridge National Laboratory

  • D. K. Christen

    • Oak Ridge National Laboratory

  • E. D. Specht

    • Oak Ridge National Laboratory

  • R. Jin

    • Oak Ridge National Laboratory
    • Materials Science \& Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • Brian C. Sales

    • Oak Ridge National Laboratory
    • Materials Science \& Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • Michael A. McGuire

    • Oak Ridge National Laboratory
    • Materials Science \& Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • A. Sefat

    • Oak Ridge National Laboratory
    • Materials Science \& Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

  • D. G. Mandrus

    • Oak Ridge National Laboratory
    • Oak Ridge National Laboratory, University of Tennessee
    • Materials Science \& Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA