Magnetic flux pinning in proton-irradiated thick Nb samples
Very pure annealed Nb samples having a resistivity ratio, GAMMAequivalentrho/sub 296//rho/sub 4.2/, in the range 1300--1700 were irradiated with 3--8-MeV protons to fluences of 6.8 x 10/sup 16/ and 3.4 x 10/sup 16/ protons/cm/sup 2/. Local magnetic induction profiles, when the samples were in the superconducting mixed state, were obtained using the ac technique of Rollins, Kuepfer, and Gey. Electron micrographs of the irradiated samples show that the damage caused by proton irradiation was inthe form of dislocation loops. The volume pinning force F/sub v/, calculated for the dislocation loops using flux pinning models and theories for b=0.7 and T=4.2 K, is compared with the experimentally obtained F/sub v/. The F/sub v/ calculated from direct summation law is an order of magnitude higher than the experimental result and the F/sub v/ calculated from models, which use Labusch quadratic summation law, is two to three orders of magnitude smaller than the experimental value. Our experimental pinning force per dislocation loop is in agreement with a master curve obtained by Kramer as an empirical solution to the summation problem. Experimentally obtained F/sub v/, for temperatures lying betweeen 2 and 7 K obey a scaling law. If the temperature dependence is written as F/sub v/proportionalH/sup n//sub c/, then we found n to be slightly dependent on depth x from the sample surface. At x=20 ..mu..m, n=3.2 (- 0.2; while at x=84 ..mu..m, n=2.7 +- 0.2. The experimental scaling law is compared with the scaling laws obtained from the Labusch model for point pinning centers and Kramer's model for line pinning centers. Irradiated samples were observed to have a region at the surface with no apparent pinning. This observation is discussed in terms of two different effects: (i) reversible motion of flux lines and (ii) a threshold for flux pinning.
- Research Organization:
- Department of Physics, Ohio University, Athens, Ohio 45701
- OSTI ID:
- 6511313
- Journal Information:
- J. Appl. Phys.; (United States), Journal Name: J. Appl. Phys.; (United States) Vol. 50:1; ISSN JAPIA
- Country of Publication:
- United States
- Language:
- English
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360106* -- Metals & Alloys-- Radiation Effects
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
BEAMS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DISLOCATIONS
ELECTRON MICROSCOPY
ELEMENTS
IRRADIATION
LINE DEFECTS
MAGNETIC FLUX
METALS
MICROSCOPY
NIOBIUM
NUCLEON BEAMS
PARTICLE BEAMS
PHYSICAL RADIATION EFFECTS
PROTON BEAMS
RADIATION EFFECTS
REFRACTORY METALS
SUPERCONDUCTORS
TEMPERATURE DEPENDENCE
TRANSITION ELEMENTS
TYPE-II SUPERCONDUCTORS