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The trapped magnetic field is examined in bulk high-temperaturesuperconductors that are artificially drilled along their c-axis. The influenceof the hole pattern on the magnetization is studied and compared by means ofnumerical models and Hall probe mapping techniques. To this aim, we considertwo bulk YBCO samples with a rectangular cross-section that are drilled each bysix holes arranged either on a rectangular lattice (sample I) or on a centeredrectangular lattice (sample II). For the numerical analysis, three differentmodels are considered for calculating the trapped flux: (i), a two-dimensional(2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2Dfinite-element model neglecting demagnetizing effects but incorporatingmagnetic relaxation in the form of an E-J power law, and, (iii), a 3D finiteelement analysis that takes into account both the finite height of the sampleand flux creep effects. For the experimental analysis, the trapped magneticflux density is measured above the sample surface by Hall probe mappingperformed before and after the drilling process. The maximum trapped fluxdensity in the drilled samples is found to be smaller than that in the plainsamples. The smallest magnetization drop is found for sample II, with thecentered rectangular lattice. This result is confirmed by the numerical models.In each sample, the relative drops that are calculated independently with thethree different models are in good agreement. As observed experimentally, themagnetization drop calculated in the sample II is the smallest one and itsrelative value is comparable to the measured one. By contrast, the measuredmagnetization drop in sample (1) is much larger than that predicted by thesimulations, most likely because of a change of the microstructure during thedrilling process.

Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes