Relation between magnetic entropy and resistivity in La0.67Ca0.33MnO3

We present an investigation of the magnetic entropy DeltaS and resistivity rho, and the relation between them, for La0.67Ca0.33MnO3 film. We found that the maximum DeltaS is approximately 6 J/kg(.)K, and the maximum magnetoresistance (defined as rho(0)/rho(H) - 1) is about 400% under a field mu(o)H of 5 T. A careful analysis gives an equation of the form DeltaS = -alpha integral(o)(H) [partial derivative ln(rho) / partial derivativeT] (H)dH (alpha = 21.74 emu/g), which relates magnetic order to transport behavior of the compounds. This result reveals the predominant role of magnetic polarons on the magnetoresistive property of manganites. It also provides an alternative method to determine magnetic entropy change on the basis of resistive measurements.