Effects of a ferromagnetic substrate on hysteresis losses of a YBa ₂Cu₃O₇ coated conductor in perpendicular ac applied magnetic fields

The effects of a ferromagnetic substrate on ac losses of a YBa ₂Cu₃O₇, YBCO, coated conductor in perpendicular ac magnetic fields were investigated by measuring the losses of a set of the specimens which were made by placing one Ni-5 at. % W tape on one or both sides of a YBCO layer on a Hastelloy tape. For applied field amplitude, μ₀H₀, < ∼ 5 mT, the losses with the Ni-W tape(s) were higher than those of the YBCO tape, but for ∼ 5 mT < μ₀H₀ < ∼ 0.1 T, the losses were reduced by putting the Ni-W tape(s) on the YBCO tape. For μ₀H₀ > ∼ 0.1 T, the losses became the same for all of the specimens. Also, the geometric actor χ₀ of the susceptibility χ was determined from the hysteresis loops for these specimens, and was found to decease with the addition of the magnetic substrate. These observations agreed very well with the theoretical calculations for the losses and χ₀ for a YBCO layer on a ferromagnetic substrate by Y Mawatari (unpublished).