Measurement of magnetic hysteresis loops of the Ni-5at.%W alloy substrate as a function of temperature in a stack of 2G HTS coated conductor annuli

The development of coated conductors with a ferromagnetic substrate and their use in various applications require an accurate knowledge of the magnetic properties of the substrate. In this work, we report measurements in AC regime (30 Hz) of the magnetic hysteresis loops of the Ni-5at.%W alloy ferromagnetic substrate in a stack of 2G YBCO tapes cut in the shape of annuli from 46 mm wide coated conductors. The stacked annuli form a closed magnetic circuit which is the ideal configuration due to the absence of demagnetizing effect. The measurements are carried out at four temperatures between 77 K and 293 K. The peak intensity of the relative permeability is not significantly affected in the range of temperature considered. The coercive field dependence with temperature is also investigated. The hysteresis losses Q as a function of the amplitude of the flux density Bm exhibit a power law behavior (Q ∼ B n m) at the four temperatures. This power law behavior is also studied at low fields under the presence of a DC bias field. Finally, the hysteresis loops can be reproduced with the Jiles-Atherton model, which is used to estimate the hysteresis parameters and to discuss their temperature dependence.