Critical behaviors in double-exchange ferromagnets Pr1−xPbxMnO3

Two polycrystalline samples Pr1−xPbxMnO3 (x = 0.1 and 0.2) were prepared by solid-state reaction. Experimental results reveal that all of them undergo a second-order magnetic phase transition. By using the modified Arrott plot method, the critical parameters were obtained to be TC ≈ 150.6 K, β = 0.443 ± 0.027, γ = 1.337 ± 0.042, and δ = 3.99 ± 0.07 for x = 0.01, and TC ≈ 203.8 K, β = 0.468 ± 004, γ = 1.353 ± 0.083, and δ = 3.78 ± 0.02 for x = 0.02. With these critical exponents, the isothermal magnetization data of the samples around TC fall into two branches of a universal function M(H,e) = |e|βf±(H/|e|β+γ), where e = (T − TC)/TC is the reduced temperature, f+ for T > TC, and f− for T < TC. This proves that the critical parameters determined are reliable, and in good accordance with the scaling hypothesis. Here, the values of β obtained for our samples are located in between those expected for the mean-field theory (β = 0.5) and the Heisenberg model (β = 0.365). Such results demonstrate an existence of f...