The thermally induced flux motion and the elemental pinning force, fp, for Nb thin films (1000-5000A) were measured for applied magnetic fields ranging from 0.3 to 7.5G, and temperatures from 4.22K to 5.72K. / The magnitude of f$\sb{\rm p}$(H,d,T) ranged from 10$\sp{-12}$ to 10$\sp{-11}$ N/m which is approximately 5 orders of magnitude smaller than Lorentz force depinning measurements made on Nb for the high field regime$\sp{16}$ (flux line lattice), as well as the low field regime$\sp{15}$ (isolated essentially non-interacting fluxoids). Some of these results are similar to the works of Huebener, et al, who first found a large discrepancy between the transport current method (J x B) and the thermal method, S$\nabla$T, when calculating the pinning force on a flux line lattice structure. A model was proposed to explain the discrepancy in terms of an electron scattering effect at or near the grain boundaries and extending into the grains which produces a channeling effect whereby the transport electrons flow away from the trapped fluxoids such that their local Lorentz force per unit length is less than the value calculated from J$\sb{\rm ave\Phi o}$. / The $\Delta\Phi$ vs $\Delta$T data for small $\Delta$T values, implied a spectrum of pinning force values where the fluxoids that were depinned and had substantially weaker pinning forces than the majority of the remaining trapped flux lines. Using statistical arguments, the qualitative features of the $\Delta\Phi$(H,d) data and f$\sb{\rm p}$(H,d) is explained. The data exhibited a magnetic field threshold, below which there is no flux motion for the temperature range studied. The value of the minimum required applied field necessary for flux motion increases with increasing thickness. / Source: Dissertation Abstracts International, Volume: 49-12, Section: B, page: 5358. / Major Professor: William G. Moulton. / Thesis (Ph.D.)--The Florida State University, 1988.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_77912 |
| Contributors | Goldstein, Michael Jay., Florida State University |
| Source Sets | Florida State University |
| Language | English |
| Detected Language | English |
| Type | Text |
| Format | 173 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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