THERMAL-PROPERTIES OF SOME RE(1-X)EA(X)MNO(3) COMPOUNDS

The Seebeck- effect and the thermal diffusivity kappa of epitaxial lay ers of La0.67Ca0.33MnO3-gamma and bulk samples of Nd0.67Sr0.33MnO3-del ta were investigated in the temperature range 35K < T < 300K using the time resolved thermoelectric power (flash) method. In the temperature regime of the high magnetoresistance (GMR) which is close to the maxi mum resistivity rho(max). Of the La-Ca compound, we find a sign change of S(T) and a step in heat conductivity which we attribute to a tempe rature - induced metal-insulator transition at about 80K. For Nd0.67Sr 0.33MnO3-delta such a transition is also observed, but around 160K; he re S(T) is always positive except for a gradual sign change at 370 K a nd the changes in kappa are also more gradual. For temperatures above rho(max) we find evidence of a spin glass like state in both cases.