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

Abstract

We have studied the influence of the Cu-doping on the critical properties of a polycrystalline sample of La0.7Ca0.3Mn0.95Cu0.05O3 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 TC ≈ 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, e) = eβf±(H/eβ+γ), where e = (T - TC)/TC (the reduced temperature), f+ for T >; TC and f_ for T <; TC. 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 La0.7Ca0.3Mn0.95Cu0.05O3 while the parent compound of La0.7Ca0.3MnO 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.