Thermal Material With Low Curie Temperature in a Thermally Actuated Superconducting Flux Pump System

A thermally actuated flux pump is an efficient method to magnetize the high-temperature superconductor (HTS) bulk without applying a strong magnetic field. A thermal material is employed as a magnetic switch, which decides the efficiency of the system. To measure the Curie temperatures of those samples without destroying them, the nondestructive Curie temperature (NDT) measurement was developed. The Curie temperature of gadolinium (Gd) was measured by the NDT method and compared to the results from superconducting quantum interference device (SQUID). Because the SQUID tests require the sample to be cut into small piece, a constant shape of the testing sample could not be guaranteed. The demagnetizing effect was considered to remove the shape effect. The intrinsic permeability was modified from the apparent susceptibility by considering demagnetization. A thermal material with low Curie temperature, Mg_0.15Cu_0.15Zn_0.7Ti_0.04 Fe_1.96O₄, was synthesized and its performance was tested and compared with previous thermal materials. Comparisons of three thermal materials, including the Curie temperature and the permeability, will be detailed in the paper.