Thermal properties of Ti-doped Cu–Zn soft ferrites used as thermally actuated material for magnetizing superconductors

A great majority of widely used ferrite ceramics exhibit a relatively high temperature of
order–disorder phase transition in their magnetic subsystem. For applications related to the
magnetization process of superconductors, however, a low value of Tc is required. Here we
report and analyze in detail the thermal properties of bulk Ti-doped Cu–Zn ferrite ceramics
Cu0.3Zn0.7Ti0.04Fe1.96O4 and Mg0.15Cu0.15Zn0.7Ti0.04Fe1.96O4. They are characterized by a Curie
temperature in the range 120–170 K and a maximum DC magnetic susceptibility exceeding
20 for the Cu0.3Zn0.7Ti0.04Fe1.96O4 material. The temperature dependence of both the specific
heat Cp and of the thermal conductivity κ, determined between 2 and 300 K, are found not
to exhibit any peculiar feature at the magnetic transition temperature. The low-temperature
dependence of both κ and the mean free path of phonons suggests a mesoscopic fractal
structure of the grains. From the measured data, the characteristics of thermally actuated
waves are estimated. The low magnetic phase transition temperature and suitable thermal
parameters make the investigated ferrite ceramics applicable as magnetic wave producers in
devices designed for magnetization of high-temperature superconductors.