  Applying a magnetic field to a solid changes its thermal-transport
properties. Although such magneto-thermal-transport phenomena are usually small
effects, giant magneto-thermal resistance has recently been observed in
spintronic materials1,2 and superconductors3,4, opening up new possibilities in
thermal management technologies. However, the thermal conductivity
conventionally changes only when a magnetic field is applied due to the absence
of nonvolatility, which limits potential applications of thermal switching
devices5,6. Here, we report the observation of nonvolatile thermal switching
that changes the thermal conductivity when a magnetic field is applied and
retains the value even when the field is turned off. This unconventional
magneto-thermal switching, surprisingly, arises in commercial Sn-Pb solders and
is realized by phase-separated superconducting states and resultant nonuniform
magnetic flux distributions. This result confirms the versatility of the
observed phenomenon and aids the development of active solid-state thermal
management devices.
