Speaker
Martin Nikolo
(Saint Louis University)
Description
Thermally assisted flux flow (TAFF) based on magneto-resistivity and ac susceptibility measurements is studied in a Ba(Fe0.91Co0.09)2As2 (Tc = 25.3 K) sample in magnetic fields up to 18 T. In addition to the upper critical field µ0Hc2 and the coherence length ξ(0), the flux flow activation energy U(T,H) has also been determined. The resistive transition width is proportional to µ0H, in contrast to Tinkham’s theoretical prediction. By applying Fisher's model, the glass melting transition temperature Tg, which occurs in the upper TAFF state and not in the zero resistivity vortex solid regime, is calculated. The onset of TAFF temperature and the crossover temperature Tx from TAFF to flux flow are determined. By contrasting the ac susceptibility data with the resistivity data, considerable flux penetration appears even in the zero resistivity state, in addition to ac losses. The H-T phase diagram is drawn and shows weak pinning regime as the field approaches µ0Hc2, and the strength of the weak pinning decreases to zero with increasing magnetic field from 0 T to 18 T.
Author
Martin Nikolo
(Saint Louis University)
Co-authors
Prof.
Eric Hellstrom
(Applied Superconductivity Center, NHFML, FSU)
Dr
Eun Choi
(National High Field Magnet Lab, FSU)
Dr
Jeremy Weiss
(Applied Superconductivity Center, NHFML, FSU)
Dr
Jianyi Jiang
(Applied Superconductivity Center, NHFML, FSU)
Dr
Xiaoyan Shi
(National High Field Magnet Lab, FSU)
