Critical Behavior of Ni-doped La0.7Sr0.3MnO3 Ceramics

The effect of Ni substitution on the magnetic properties and the critical behavior of La 0.7 Sr 0.3 Mn 1− x Ni x O 3 compounds, which were prepared by the solid-state reaction method has been investigated. Based on our investigations of the temperature and the magnetic field dependences of magnetization M ( T , H ) data, it is shown that the Curie temperature ( T C ) of La 0.7 Sr 0.3 Mn 1− x Ni x O 3 compounds will be shifted toward room temperature with increasing Ni concentration ( x ), T C = 359–307 K for x = 0.0–0.1. By using the modified Arrott plots and the Kouvel–Fisher methods together with M ( H , T ) data in the vicinity of the ferromagnetic (FM)–paramagnetic phase transition, the critical exponents ( β , γ , and δ ) have been determined. Our results show the existence of a short-range FM order in the undoped sample ( x = 0). The values of β , γ , and δ will be shifted gradually toward those of the mean-field theory when x increases, suggesting that the long-range FM order is favored in Ni-doped samples. The results calculated on the effective exponents of β eff ( ε ) and γ eff ( ε ) in the asymptotic region indicate the existence of a magnetic disorder in all the samples.