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# Anomalous d.c. field dependence of non-resonant r.f. absorption at high r.f. fields in $YBa_2Cu_3O_{7_\delta}$ powders

Srinivasu, VV and Bhat, SV and Kumar, N (1994) Anomalous d.c. field dependence of non-resonant r.f. absorption at high r.f. fields in $YBa_2Cu_3O_{7_\delta}$ powders. In: Solid State Communications, 89 (4). pp. 375-378.

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## Abstract

We have measured r.f. absorption at 14 MHz in powdered samples of sintered $YBa_2Cu_30_{7-\delta}$ at 77K $(T_c\approx 90 K)$ as function of low d.c. scan field $(H_{dc})$ for different amplitudes of the r.f. field $(H\omega)$. At low $H\omega\sim 4mG$, we obtained the well known non-resonant r.f. absorption that increased monotonically with $|H_{dc}|$ $(<{\sim}30G)$. At higher r.f. fields $(H\omega \geq20 mG)$, however, the phase of the derivative signal with respect to the d.c.-field $(H_{dc})$ scan reversed implying decreasing r.f. absorption with increasing $|H_{dc}|$. This anomalous $H_{dc}$ dependent r.f. absorption at higher $H\omega$ may be understood in terms of a non-linear response of weakly-connected superconducting rings distributed in the powdered sample. Here, the r.f. induced supercurrents drive the damped fluxons pinned in the Josephson junctions assumed to be non-hysteretic. The anomaly is absent in well sintered bulk samples.

Item Type: Journal Article Copyright of this article belongs to Elsevier. Division of Physical & Mathematical Sciences > Physics 16 Oct 2006 19 Sep 2010 04:30 http://eprints.iisc.ernet.in/id/eprint/8249

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