Observation of giant nonvolatile magneto-thermal switching in superconductor-ferromagnet hybrids
Magneto-thermal switch is a crucial thermal component which enables heat transfer control by the application of an external magnetic field. Recently, a nonvolatile behavior in magneto-thermal conductivity at zero magnetic field was observed in type-II and phase-separated superconductors owing to magnetic flux pinning nature, leading to an energy-efficient thermal control technology. However, the nonvolatile magneto-thermal switching ratio has been much lower than the volatile one in conventional materials. Here, we demonstrate a giant nonvolatile magneto-thermal switching in ferromagnetic Fe-superconducting Pb hybrids. The dispersion of pure Fe particles realizes increased electron and decreased phonon contributions in the thermal conductivity, which enhances the magneto-thermal switching ratio at the superconducting-to-normal conducting phase transition. Furthermore, in concert with trapped magnetic flux by supercurrent, ferromagnetic moment of Fe breaks the superconductivity of Pb matrix at zero magnetic field, enabling a significantly large nonvolatility even with a slight amount of Fe inclusions. Consequently, the nonvolatile magneto-thermal switching ratio reaches 719% in maximum at the Fe ratio of 8.7 vol%, which is more than twice the previous record value observed in Pb-Sn composites and the volatile one in pure Pb. This work broadens the exploration space and strategy for giant nonvolatile magneto-thermal switching materials.