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

We present an investigation of the magnetic entropy ΔS and resistivity ρ, and the relation between them, for La_0.67Ca_0.33MnO₃ film. We found that the maximum ΔS is approximately 6 J/kg·K, and the maximum magnetoresistance (defined as ρ(0)/ρ(H)-1) is about 400% under a field μ_oH of 5 T. A careful analysis gives an equation of the form ΔS=-α∫₀^H[∂ln(ρ)/∂T]_HdH (α=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.