technique the insulating portions 151 152 and 153 fig8 a 8b 8c 9a and 9b of the heat commutator 160 are preferably made from a material having a low thermal conductivity and or being substantially thermally insulating when the insulating portions 151 152 and 153 are made of a suitable thermoplastic material they may be molded directly onto the thermally conductive core 164 the permanent magnets 146 may be installed in the pockets 180 within the thermally conducting core 164 see fig1 a 10b 10c and 11 prior to installation of the insulating portion 153 preferably the insulating portions 153 seal the magnets 146 in their pockets 180 to prevent their exposure to the tif the permanent magnets 146 may be of the rare earth type such as a neodymium iron boron ndfeb composition having a remanent magnetic flux density in excess of 1 4 tesla but other types of permanent magnets may be also practiced with the subject invention preferably the permanent magnets 146 are arranged to fit tightly into the pockets 180 to provide good thermal communication therebetween the magnetization vectors 186 of the permanent magnets 146 are preferably arranged to be perpendicular to the thermal interface surfaces 194 of the thermally conducting core 164 fig1 b the direction of the magnetization vectors 186 is generally shown in fig9 b where the symbol u201c u2022 u201d represents a magnetization vector being normal to the drawing sheet and pointing out toward the viewer and the symbol u201c 0 u201d represents a magnetization vector being normal to the drawing sheet and pointing in away from the viewer when the.