Surface and subsurface oxygen vacancies on the slightly reduced CeO(2)(111) surface have been studied by atomic resolution dynamic force microscopy at 80 K. Both types of defect are clearly identified by the comparison of the observed topographic features with the corresponding structures predicted from recent first-principles calculations. By combining two simultaneously acquired signals (the topography and the energy dissipated from the cantilever oscillation), we are able to unambiguously locate subsurface oxygen vacancies buried at the third surface atomic layer. We report evidence of local ordering of these subsurface defects that suggests the existence of a delicate balance between subtle interactions among adjacent subsurface oxygen vacancy structures.

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The development of NMR/MRI REBa2Cu3Oy (REBCO, RE = Rare Earth) magnets is undergoing all over the world. However, a screening current-induced magnetic field (SCMF) is a serious problem for NMR/MRI magnets wound with REBCO tapes. The reduction of SCMF is strongly desired, and the estimation of SCMF is also desired at the design stage of REBCO magnets. In order to evaluate a SCMF, a finite element method (FEM) or a boundary integration method is needed so far, and a high-level simulation technique is required. In this paper, we develop an easy method to estimate a SCMF without any high-level simulation technique. In the developed method, an inductance of a winding turn is calculated and then a screening current is estimated according to the magnetic field penetrating into the winding turn. The SCMF is obtained from the estimated screening current. The SCMFs computed by the proposed method were compared with measurements and simulation results of the FEM. The results agreed well, but we can see a large difference. However, the SCMFs by the proposed method are enough accurate so that we know the SCMFs at the design stage without using a high-level simulation technique.

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