HEAT DIFFUSIVITY OF LA1-XCAXMNO3 EPITAXIAL LAYERS

The Seebeck effect and the thermal diffusivity La0.67Ca0.33MnO3-delta were investigated in the temperature range 35 < T < 300 K and in parti cular in the regime of the high magnetoresistance and maximum resistiv ity rho(max). We find a sign change of the thermoelectric power S(T) a nd a step in heat conductivity near rho(max) which we attribute to a t emperature-induced metal-insulator transition at about 80 K, suggestin g that the large giant magnetoresistance found in these substances is due to a field-induced metal-insulator transition. (C) 1996 American I nstitute of Physics.