Neutron Diffraction Study of Magnetic Flux-Line Lattice Structures in High Temperature Superconducting Oxides.

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For the first 2 years of this project we have applied a method of small angle neutron scattering and for the last 1 year another method of depolarization measurement of transmitted neutrons in order to study the magnetic flux-line lattice structures in superconducting oxides YBa_2Cu_3O_7 or Bi_2SrCaCu_2O_8.In the first method after confirming that we can observe a Bragg peak from the magnetic tlux-line lattice structures in superconducting metal niobium, we tried to measure in similar experimental conditions a Bragg peak from those in superconducting oxides. However we failed to observe it, because the Landau-Ginzburg parameter kappais 100 for the oxides in comparison with that of 4 in niobium metal.Then we changed to the second method in which we measured the depolarization of almost 100% polarized neutrons that were transmitted through the superconducting oxides. We found that the depolarization of neutrons was very much sensitive to the state of the magnetic flux-line lattice structures.From this experiment we observed the dependence of the depolarization of neutrons on a change of the magnetic field applied to the samples, a change of the temperature of the samples and also an elapsed time at constant temperature after it was changed.In conclusion, we have found that several experimental conditions must be fulfilled in order to measure a Bragg peak from the magnetic flux-line lattice structure in the superconducting oxides, and that the observation of the depolarization of polarized neutrons through the superconducting oxides provides a very sensible tool to examine and characterize the state of the magnetic flux-line lattice structures.