We have used a critical behavior study of La0.7Ca0.3MnO3 (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 TC = 185 K, β = 0.331 ± 0.019, and γ = 1.15 ± 0.017; and TC = 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 (TC) was split into a universal function with two branches M(H,ϵ) = |ϵ|βf±(H/|ϵ|β+γ), where ϵ=(T-TC)/TC is the reduced temperature. f+ is used when T>TC, while f+ is used when T<TC. 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.
Nanto, D., Kurniawan, B., Soegijono, B., Ghosh, N., Hwang, J. S., & Yu, S. C. (2018). Critical exponent analysis of lightly germanium-doped La0.7Ca0.3Mn1- xGexO3 (x = 0.05 and x = 0.07). AIP Advances, 8(4). https://doi.org/10.1063/1.4993412