Crossing point of the magnetization versus temperature curves and the meissner fraction in granular (formula presented) superconductors: Random orientation and inhomogeneity effects

Physical Review B - Condensed Matter and Materials Physics

Volumn 59, Issue 6, 1999, Pages 4394-4403

  Mosqueira, J ^a   Ramallo, M V ^a   Revcolevschi, A ^b   Torron C ^a   Vidal, Félix ^a  

^a UNIVERSITY OF SANTIAGO DE COMPOSTELA   (Spain)

^b UNIVERSITÉ PARIS SUD   (France)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 0000839361     PISSN: 10980121     EISSN: 1550235X     Source Type: Journal    
DOI: 10.1103/PhysRevB.59.4394     Document Type: Article

References (36)

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17. J.-Y. Genoud, G. Triscone, A. Junod, T. Tsukamoto, and J. Muller, Physica C 242, 143 (1995). It was concluded in this paper that any correction for extrinsic inhomogeneity effects through the measured Meissner fraction will increase the disagreement between the excess magnetization at the crossing point that they measure in ceramic (Formula presented) (Bi-2212) samples and the theoretical prediction [Eq. (1)]. It seems that these authors arrive at this conclusion because they do not correct the measured field-cooled magnetization from random orientation effects. Instead, they introduce only a correction for demagnetizing effects, and in addition through an expression which is applicable only to single crystals or grain aligned samples. Such a correction, is equivalent to use in Eq. (12), (Formula presented) instead of (Formula presented) This leads to very different values of the correction factor in Eq. (12). Although Eq. (12) applies only to randomly oriented uncoupled grains, it may also be a reasonable approximation for ceramic samples provided that the applied magnetic field has enough amplitude to decouple the grains. This seems to be the case in the measurements of these authors. For instance, for the ceramic Bi-2212 sample noted “ceram-2,” whose data are given in Figs. 22 and 55 of the Genoud et al. paper, (Formula presented) which through Eq. (12) leads to a correction factor of the order of 1, whereas the procedure proposed by these authors leads to a correction factor of the order of 0.4. Such a difference, somewhat larger than a factor of 2, is just the disagreement factor claimed by these authors between their data and the theoretical proposal [Eq. (1)].
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36. If the measurement is performed by first field cooling the sample and then taking the data as the sample is rotated [see, e.g., S. K. Hasanain, S. Manzoor, and M. Aftab, Physica C 272, 43 (1996)], the flux trapped during the field-cooling process would rotate solidarily with the sample, resulting in an erroneous measurement of the true FC magnetization.