Critical exponent analysis of lightly germanium-doped La_0.7Ca_0.3Mn_{1- x}Ge_xO₃ (x = 0.05 and x = 0.07)

We have used a critical behavior study of La_0.7Ca_0.3MnO₃ (LCMO) manganite perovskites whose Mn sites have been doped with Ge to explore magnetic interactions. Light Ge doping of 5 or 7 percent tended to produce LCMOs with second order magnetic transitions. The critical parameters of 5- and 7-percent Ge-doped LCMO were determined to be T_C = 185 K, β = 0.331 ± 0.019, and γ = 1.15 ± 0.017; and T_C = 153 K, β = 0.496 ± 0.011, and γ = 1.03 ± 0.046, respectively, via the modified Arrott plot method. Isothermal magnetization data collected near the Curie temperature (T_C) was split into a universal function with two branches M(H,ϵ) = |ϵ|^βf_±(H/|ϵ|^β+γ), where ϵ=(T-T_C)/T_C is the reduced temperature. f₊ is used when T>T_C, while f+ is used when T<T_C. Such results demonstrate the existence of ferromagnetic short-range order in lightly Ge-doped LCMOs. Notably, doping with Ge at high concentrations tends to generate long-range ferromagnetic order.