Heat diffusivity of Nd1-xSrxMnO3-delta and La1-xCaxMnO3-delta compounds

The thermal diffusivity of bulk and epitaxial layer samples of the giant ma gnetoresistance compounds Nd0.67Sr0.33MnO3-delta and La0.67Ca0.33MnO3-delta is investigated in a comparative study for temperatures between 35 and 350 K in order to detect preparational differences and to correlate the therma l transport with magnetization hi and resistivity rho, We find for Nd-Sr an anomaly of the heat diffusivity D near 145 K (80 K La-Ca) which we attribu te to a temperature-induced canted metal to AFM insulator transition and a second anomaly in D(T) near 250 K (300 K) which we assign to the transition to paramagnetism. The low-temperature anomaly can be a step of up to five times in the heat conductivity, which makes these compounds potential magne tic field activated heat switches, as this transition can also be induced b y a magnetic field. (C) 1998 American Institute of Physics. [S0021-8979(98) 44811-4].