Magnetic Properties of Superconducting Materials

Koblischka, Michael Rudolf; Koblischka-Veneva, Anjela

doi:10.1007/978-981-19-1211-5_3

Cited by 1 publication

(1 citation statement)

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“…The green arrow indicates where FC-C and FC-W measurements are crossing the phase diagram. H irr (T) is for most metallic superconductors very close to H c2 (T) [147]. Note also that in the field-cooling experiments with a magnetic field applied, there is always magnetic flux in the sample, and a pure Meissner state will not be reached even if flux is expelled from the sample.…”

Section: Observation Of Pme-superconducting Transitionsmentioning

confidence: 87%

The Paramagnetic Meissner Effect (PME) in Metallic Superconductors

Koblischka

Půst

Chang

et al. 2023

Metals

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The experimental data in the literature concerning the Paramagnetic Meissner Effect (PME) or also called Wohlleben effect are reviewed with the emphasis on the PME exhibited by metallic, s-wave superconductors. The PME was observed in field-cool cooling (FC-C) and field-cool warming (FC-W) m(T)-measurements on Al, Nb, Pb, Ta, in compounds such as, e.g., NbSe2, In-Sn, ZrB12, and others, and also in MgB2, the metallic superconductor with the highest transition temperature. Furthermore, samples with different shapes such as crystals, polycrystals, thin films, bi- and multilayers, nanocomposites, nanowires, mesoscopic objects, and porous materials exhibited the PME. The characteristic features of the PME, found mainly in Nb disks, such as the characteristic temperatures T1 and Tp and the apparative details of the various magnetic measurement techniques applied to observe the PME, are discussed. We also show that PME can be observed with the magnetic field applied parallel and perpendicular to the sample surface, that PME can be removed by abrading the sample surface, and that PME can be introduced or enhanced by irradiation processes. The PME can be observed as well in magnetization loops (MHLs, m(H)) in a narrow temperature window Tp<Tc, which enables the construction of a phase diagram for a superconducting sample exhibiting the PME. We found that the Nb disks still exhibit the PME after more than 20 years, and we present the efforts of magnetic imaging techniques (scanning SQUID microscopy, magneto-optics, diamond nitrogen-vacancy (NV)-center magnetometry, and low-energy muon spin spectroscopy, (LE-μSR)). Various attempts to explain PME behavior are discussed in detail. In particular, magnetic measurements of mesoscopic Al disks brought out important details employing the models of a giant vortex state and flux compression. Thus, we consider these approaches and demagnetization effects as the base to understand the formation of the paramagnetic signals in most of the materials investigated. New developments and novel directions for further experimental and theoretical analysis are also outlined.

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Section: Observation Of Pme-superconducting Transitionsmentioning

confidence: 87%