Critical behavior and change in universality of La_0.67Ba_0.22Sr_0.11Mn_1−x Co _x O₃ manganites

The critical properties of the manganese perovskite La_0.67Ba_0.22Sr_0.11Mn_1−x Co _x O₃ (x = 0.0, 0.2 and 1.0) were investigated by analyzing the magnetic data and determining the critical exponents using different techniques such as Arrott–Noakes plots, plots of Kouvel–Fisher critical isotherms and scale analysis. The analysis indicated that the experimentally determined critical exponents of the compound La_0.67Ba_0.22Sr_0.11MnO₃ belong to the three-dimensional Heisenberg universality. However, the samples doped with Co (x = 0.2 and 1.0) were characterized by critical exponents belonging to the universality class of the long-range mean field theory. The observed transition in the universality of the manganite perovskite upon doping with Co could be due to the development of long-range dipolar interactions between the spins instigated by ionic disorder, and the increase in the number of localized e _g and t _2g electrons. The doping also resulted in progressive breaking Mn⁴⁺–O–Mn³⁺ links at the substituted sites as the Co concentration increased, resulting in a significant reduction in the saturation magnetization and the ferromagnetic correlation length.