Ac loss characteristics of YBCO superconducting tapes fabricated by TFA-MOD technique

We investigated the ac loss properties of a YBCO superconducting tape fabricated by TFA-MOD technique. The thickness of the YBCO layer is 1.2 μm. A 6-tape stack of 50 mm in length and 10 mm in width was inserted into a saddle-shaped pickup coil. The ac loss was measured at 35-77 K by applying an external ac magnetic field. The magnetic field angle was changed by rotating the sample stack around its longitudinal axis. The effective penetration field, which corresponds to the breaking point of an ac loss curve, decreased with increasing field angle though it was much smaller than that which was estimated for a superconducting slab with the same thickness as the width of a tape. As a result, the ac loss increased monotonically with an increasing field angle against the wide surface for any amplitude. The observed field angular dependence of the ac loss agreed with the theoretically predicted one by using the observed ac losses in perpendicular magnetic field. Anyway the ac loss for a larger amplitude than the effective penetration field was proportional to the critical current density and the projective width of a tape in the direction of the applied magnetic field for any field angle and any temperature as well known. In addition we estimated the magnetic field, B, dependence of the critical current, Ic, from the observed magnetization curves. It was shown that zero-field Ic appeared to be a linear function of temperature and Ic-B characteristics was scaled with zero-field Ic. We also discussed a difference in Ic-B characteristics and its temperature dependence between TFA-MOD tapes and IBAD-PLD ones.