As the performance of various electronic devices increases, the need to develop materials that can change their thermal conductivity in the magnetic and electric fields has arisen. New materials that can perform "magneto-thermal switching" under magnetic fields and magnetization are one such type of materials that is under development. However, it has been difficult to realize "nonvolatile magneto-thermal switching," in which the thermal conductivity change caused by the application of a magnetic field can be maintained even after the magnetic field is turned off.
Associate Professor Yoshikazu Mizuguchi and his research team at the Graduate School of Science at Tokyo Metropolitan University, focused on a Sn-Pb solder, a composite material in which tin (Sn) and lead (Pb) are completely phase-separated. When the solder was cooled below minus 265 degrees Celsius in the absence of an external magnetic field, "perfect diamagnetism," a characteristic of superconductivity that completely excludes external magnetic fields from the material, was observed throughout the sample. At the same time, thermal conductivity became low. Then, when a magnetic field was applied, Sn and Pb ceased to be superconductive, and their thermal conductivity increased. Normally, with the removal of the magnetic field, they return from this state to the superconducting state again. However, due to the nature of the solder, in which Sn and Pb are completely phase-separated, Pb returned to the superconductive state while Sn lost its superconductivity and became a magnet as a result of the "magnetic flux-trap phenomenon" by which some magnetic flux remains without being discharged to the outside after demagnetization. The high thermal conductivity of Sn after demagnetization allows the entire solder to maintain a high thermal conductivity state, making it a nonvolatile magneto-thermal switching material.
This phenomenon is caused by the fact that the solder is a fully phase-separated composite material comprising two types of superconductors. Thus, this phenomenon will not be limited to solder, but may also occur in composite materials that exhibit superconductivity. Although this result occurs only below minus 265 degrees Celsius, the superconducting transition temperature of the solder, it is expected that this method can be applied to materials with relatively high superconducting transition temperatures to create a nonvolatile new thermal switch technology that can operate at higher temperatures.
