  Thermal switching by magnetic fields is one of the important functionalities
in thermal management technologies. In low-temperature devices, superconducting
states can be used as a magneto-thermal-switching (MTS) component, because
carrier thermal conductivity (\k{appa}) is strongly suppressed in
superconducting states. Recently, we demonstrated that the MTS ratio (MTSR) of
pure Nb reached 650% at a temperature (T) of 2.5 K under a magnetic field (H)
of 4.0 kOe [M. Yoshida et al., Appl. Phys. Express 16, 033002 (2023)]. In this
study, to enrich knowledge on MTS of superconductors, the MTSRs of pure Pb
wires with 5N and 3N purities were investigated by measuring the temperature or
magnetic field dependences of \k{appa}. For 5N-Pb, a large MTSR exceeding 1000%
was observed below 3.6 K under H > 600 Oe. Although higher MTSRs were expected
at lower temperatures under H > 600 Oe, the obtained data under those
conditions were accompanied by large errors due to magnetic-field-induced huge
\k{appa} at low temperatures. In contrast, the \k{appa} for 3N-Pb were observed
to be clearly lower than that for 5N-Pb. Although the magnetic-field-induced
change in \k{appa} was small, the MTSR at T = 2.5 K was 300%. These results
suggest that Pb is a promising material for low-temperature magneto-thermal
switching because of wide-range \k{appa} tunable by magnetic field and the
purity.
