Critical behavior of the resistivity of GaMnAs near the Curie temperature

The effect of the magnetization fluctuations on the resistivity of GaMnAs near the Curie temperature TC was experimentally studied. It is shown that the determination of TC from the maximum of the temperature derivative of the resistivity is valid for the samples with a high concentration of free carries. Whereas, for the samples with low concentration of free carriers the TC coincides with the resistivity maximum. The magnetic specific heat for T>TC demonstrates the crossover from the one dimensional to the three dimensional critical behavior when the temperature become closer to the Curie temperature. This is explained by the formation of the ferromagnetic phase in the paramagnetic side of the phase transition which is started from Mn-Mn dimers oriented along one direction.