Flux flop in Y-Ba-Cu-O crystals irradiated with 5.3-GeV Pb ions

The flux-line lattice in superconductors

“…By scanning tunnelling microscopy Behler et al (1994b) see the columnar defects and the pinned flux lines on the same NbSe 2 sample. In YBCO films irradiated at various angles by heavy ions Holzapfel et al (1993) observe sharp peaks in the angledependent critical current J c (Θ) when B is parallel to the columnar pins, see also Klein et al (1993a, b). In a similar HTSC with oblique and crossed linear defects Schuster et al (1994cSchuster et al ( , 1995b observe anisotropic pinning by magneto-optics.…”

“…Long columnar pins of damaged atomic lattice were generated by high-energy heavy-ion irradiation perpendicular to the Cu-O planes in YBCO (Roas et al 1990a, Budhani et al 1992, Klein et al 1993a, c, Schuster et al 1993b, 1994c, 1995b or BSCCO (Gerhäuser et al 1992, Leghissa et al 1992, Thompson et al 1992, Schuster et al 1992a, Klein et al 1993b, c, Kummeth et al 1994, Kraus et al 1994. Clearly these linear pins are most effective when the flux lines are parallel to the pins since then large sections of the flux line are pinned simultaneously, which means a large pinning energy and a reduction of thermally activated depinning.…”

Columnar defects acting as passive internal field detectors

“…At low enough fields the lock-in angle L ϰ1/h covers most of the angular range ͑this is essentially what Klein et al 5 called flux-flop in their early work͒, thus producing a very broad plateau that turns our method inapplicable to determine ⌰ max .…”

“…1,2 In the YBa 2 Cu 3 O 7 ͑Y:123͒ compound, the directional pinning produced by these correlated structures becomes evident when the angular dependence of J c is studied. 3,4 In the last decade several works have shown that a sharp peak in J c (⌰) appears when the applied field H is aligned with the direction (⌰ D ) of these linear defects 1,3,[5][6][7][8] ͑here ⌰ and ⌰ D are the angles formed by the crystallographic c axis with H and the CD, respectively͒. However, this behavior only holds when H is high enough to ensure that the average vortex direction is parallel to H. At lower fields, both material anisotropy and geometry effects become relevant and modify the vortex orientation, 9 which consequently may not coincide with that of H. Since maximum pinning occurs when the vortex orientation ͑given by the internal field B rather than by H) is aligned with the CD, J c (⌰) should maximize at an angle ⌰ max ⌰ D .…”

Anomalous behavior of the irreversible magnetization and time relaxation inYBa2Cu3OSilhanek1, Niebieskikwiat2, Civale3 et al. 1999Phys. Rev. B90100View full textAdd to dashboardCite

“…Thus, the angular dependence of the persistent current density J should show [5][6][7] a peak at the CD's direction, as indeed observed in many cases. 1,3,4,[8][9][10][11][12][13][14][15] However, Zhukov et al 16 have recently shown that the angular dependence of the irreversible magnetization of YBa 2 Cu 3 O 7 ͑YBCO͒ crystals with CDs along the c axis exhibit a local minimum rather than a maximum for that field orientation. They found that this interesting and anti-intuitive behavior is related to geometrical effects; if the rotation axis is parallel to the shortest side of a rectangular sample, the minimum is observed, but if the axis coincides with the longest side, the usual maximum in the angular dependence is recovered.…”