Effects of the Cu Doping on Critical Behavior of ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}$

We have studied the influence of the Cu-doping on the critical properties of a polycrystalline sample of La_0.7Ca_0.3Mn_0.95Cu_0.05O₃ prepared by solid-state reaction. Analyses of static magnetization data in the vicinity of the ferromagnetic-paramagnetic phase transition based on the modified Arrott plot reveal critical parameters of T_C ≈ 197.3 K, β = 0.49 ± 0.03 and γ = 1.04 ± 0.04. These parameters are in good agreement with a magnetic equation of state M(H, ε) = ε^βf±(H/ε^β+γ), where ε = (T - T_C)/T_C (the reduced temperature), f₊ for T >; T_C and f_ for T <; T_C. Comparing with theoretical models, the critical exponents in our case are close to those expected for the mean-field theory. This reflects that the Cu doping leads to the second-order phase transition in La_0.7Ca_0.3Mn_0.95Cu_0.05O₃ while the parent compound of La_0.7Ca_0.3MnO exhibits the first-order phase transition. Such the phenomenon is assigned to changes in structural parameters, Mn³⁺/Mn⁴⁺ ratio, and magnetic interaction mechanisms caused by Cu dopants.