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Author Kostic, P. ♦ Veal, B. ♦ Paulikas, A. P. ♦ Welp, U. ♦ Todt, V. R. ♦ Gu, C. ♦ Geiser, U. ♦ Williams, J. M. ♦ Carlson, K. D. ♦ Klemm, R. A.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ PHYSICS ♦ NIOBIUM ♦ MAGNETIC PROPERTIES ♦ MEISSNER-OCHSENFELD EFFECT ♦ BCS THEORY ♦ D WAVES ♦ PARAMAGNETISM ♦ S WAVES ♦ TEMPERATURE DEPENDENCE ♦ TEMPERATURE RANGE 0000-0013 K
Abstract The paramagnetic Meissner effect (PME), or Wohlleben effect, in which the field-cooled magnetization of superconducting samples is paramagnetic below {ital T}{sub {ital c}}, has been reported to occur in some samples of a variety of high-{ital T}{sub {ital c}} cuprate superconductors. It has been proposed that the effect arose in granular hole-doped cuprates from current loops with {pi} phase shifts of the superconducting order parameter at some grain-boundary junctions. It is argued that such behavior would be expected to occur in a {ital d}-wave superconductor, but not in a conventional {ital s}-wave superconductor. To test this hypothesis, we have searched for the occurrence of the effect in Nb, and have confirmed a recent report by Minhaj {ital et} {ital al}. of its occurrence in some Nb samples. For these studies, the effects of stray fields and field gradients in the measurement volume of the superconducting quantum interference device magnetometer have been carefully considered to rule out the possibility that measurement artifacts might be responsible for the apparent paramagnetic behavior in Nb. The {ital M}({ital T}) and {ital M}({ital H}) curves obtained in Nb samples that show the PME also show remarkably strong resemblance to those curves reported for the cuprate materials exhibiting the PME. Evidence is presented that the effect arises from inhomogeneously trapped flux, and is strongly influenced by sample geometry and surface effects. These results suggest that, for the effect to be observable, {ital T}{sub {ital c}} on the sample surface must be different from the bulk {ital T}{sub {ital c}}. The occurrence of the PME in Nb strongly suggests that the observation of this effect is unrelated to {ital d}-wave superconductivity. {copyright} {ital 1996 The American Physical Society.}
ISSN 01631829
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-01-01
Publisher Place United States
Journal Physical Review, B: Condensed Matter
Volume Number 53
Issue Number 2


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