Ferromagnetic transition in a double-exchange system containing impurities

We study the ferromagnetic transition in a three-dimensional double-exchange model containing impurities. The influence of both spin fluctuations and the impurity potential on conduction electrons is described in a coherent potential approximation. In the framework of the thermodynamic approach we construct a Landau functional for the system "electrons (in disordered environment) + core spins." Analyzing the Landau functional we calculate the temperature of the ferromagnetic transition T_C and paramagnetic susceptibility χ. For T_C, we thus extend the result obtained by Furukawa in the framework of the dynamical mean-field approximation, with which our result coincides in the limit of zero-impurity potential. We find that alloy disorder, able to produce a gap in the density of election states, can substantially decrease T_C with respect to the case of no impurities.