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

Abstract

The development of coated conductors with a ferromagnetic substrate and their use in various applications require accurate knowledge of the magnetic properties of the substrate. In this work, we report measurements in the ac regime (30 Hz) of the magnetic hysteresis loops of the Ni-5at.%W alloy ferromagnetic substrate in a stack of second-generation YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (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 on temperature is also investigated. The hysteresis losses <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q$</tex-math></inline-formula> as a function of the amplitude of the flux density <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_\text{m}$</tex-math></inline-formula> exhibit a power law behavior ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$Q\sim B_\text{m}^{n}$</tex-math></inline-formula> ) 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.