Anisotropy of Superconducting Properties of a YBa2Cu3O7−x Crystal Investigated by Torque Measurements

Andrä, W.; Danan, H.; Hergt, R.

doi:10.1002/pssa.2211110224

Cited by 20 publications

(9 citation statements)

References 14 publications

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“…For rotation about an axis perpendicular to the c-axis two sharp maxima occur per cycle as we have discussed recently [9]. These maxima were seen also by other authors which give alternative explanations [16, 171.…”

Section: Spikessupporting

confidence: 78%

“…3. It was shown recently [9] . The shape of the loss curves suggests that there are two parts of losses: Sharp loss maxima are localized at certain preferential field orientations.…”

Section: Stationary Field Rotationmentioning

confidence: 90%

“…Crystals to be measured were cooled down in zero field (H = 40 A/m). Then, in order to take account of relaxational effects in these materials a well-defined quasistationary regime of measurement was followed as described previously [9]. Torque curves G(w) or G(rp), respectively, were measured for clockwise, Gcw, as well as counterclockwise, GcCw, field rotation in order to detect rotational hysteretic losses.…”

Section: Methodsmentioning

confidence: 99%

“…Recently, we found by torque measurements anisotropic losses in YBa,Cu,O, -, single crystals [9] which have been ascribed to the interaction of vortices with twin planes. Torque measurements proved to be useful for investigations ofthe pinning behaviour in conventional hard superconductors [lo] and were also applied to highT, superconductors (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Pinning in Twinned Single Crystals of Superconducting REBa2Cu3O7−x Investigated by Torque Magnetometry

Hergt

Andrä

Fischer

et al. 1990

phys. stat. sol. (a)

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Two types of single crystals REBa2Cu3O7‐x which are grown by different methods and which differ in their content of twin boundaries are investigated in the vicinity of Tc with respect to rotational hysteretic losses. Two types of frictionlike losses may be differentiated, one of which is obviously connected with the presence of twin boundaries. Losses are found to be vanishing at a temperature below Tc which may be explained by the existence of an irreversibility line. In dependence on the minor loop amplitude a transition from reversible to irreversible reversal behaviour is observed. Results may be understood by the assumption of an angular lag between vortex lines and the external magnetic field. From the field dependence of this angular lag within the ab‐plane a characteristic field is derived which has the same order of magnitude as the lower critical field. The results are discussed qualitatively in terms of the pinning potentials for the vortices.

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Section: Spikessupporting

confidence: 78%

“…3. It was shown recently [9] . The shape of the loss curves suggests that there are two parts of losses: Sharp loss maxima are localized at certain preferential field orientations.…”

Section: Stationary Field Rotationmentioning

confidence: 90%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pinning in Twinned Single Crystals of Superconducting REBa2Cu3O7−x Investigated by Torque Magnetometry

Hergt

Andrä

Fischer

et al. 1990

phys. stat. sol. (a)

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“…We have demonstrated these effects in a slab geometry, but analogous effects will be seen in all geometries. Since anisotropic materials such as the high-7V superconductors frequently possess a plate geometry, these results indicate that interpretations [1][2][3][4][5] of their irreversible magnetic behavior in terms of an intrinsic material anisotropy may need to be reexamined.…”

Section: To Understand the Experimental Results We Consider The Beanmentioning

confidence: 92%

Quasi-2D behavior in bulk isotropic type-II superconductors: Shape effects

1992

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The induced magnetization of an isotropic type-II superconductor with an anisotropic sample shape has been measured in an oblique magnetic field and separated into its reversible and irreversible contributions. The measurements unexpectedly show that the irreversible magnetization is oriented essentially parallel to the smallest sample dimension, and is almost independent of the angle of the applied field. This behavior can be understood by considering the critical-state model when the applied field is at an arbitrary direction with respect to the sample axes.PACS numbers: 74.60.Ge, 74.30.CiMuch recent work has focused on the anomalous effects of a magnetic field applied at an angle to the a-b planes of the anisotropic high-7V copper oxide superconductors [1-7]. Observed anisotropy in the irreversible (pinned) behavior is interpreted as being due to the intrinsic anisotropy of the material [1-5]. We have found, however, that when vortex pinning is present, even isotropic type-II superconductors exhibit unexpected results which can be explained as being due purely to sample shape considerations. For bulk parallelepipeds with geometrical aspect ratios as low as 2:1, the irreversible magnetization is oriented essentially parallel to the smallest dimension and does not change as the angle of the applied field is varied from perpendicular to greater than a 45° angle. This unexpected observation is shown here to result from the Bean critical-state model [8] modified to include an applied field at an angle with respect to the sample axes.The measurements were made on polycrystalline Nb and Pb-Bi alloys. The applied field H a was cycled between H C 2 and -H C 2. The induced magnetization density M, due to the macroscopic screening currents, was measured using a vibrating sample magnetometer to determine the component of M along H a , A/VSM, and a torque magnetometer to determine the component of M perpendicular to H a , M {or . All measurements were made at 4.2 K.There are two contributions to M: (a) a reversible part M r due to a screening current near the sample surface and associated with the expulsion of the magnetic field, and (b) an irreversible part M, associated with pinning of the vortices and the resultant vortex density gradient and screening current throughout the sample. The reversible contribution below H c \ equals -H/4K (the usual Meissner effect) and above H c \ is determined by the repulsive interactions of the vortices [9,10]. Demagnetization corrections due to geometry increase the absolute value of the initial slope above 1/4/r and cause M r to lie along a direction different from H a [9-11]. The irreversible contribution results from pinning of the vortices as they attempt to enter or leave the sample (in increasing or decreasing applied fields, respectively). A critical state is set up in which a vortex density gradient and a concomitant critical current J c flows throughout the sample, resulting in a magnetization A// [8,12]. The sign of the gradient, the direction of the current flow, and hence t...

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