Crossover critical behavior of Ga _1-xMn _xAs

The critical behavior of the ferromagnetic semiconductor Ga _1-xMn _xAs with different concentrations of Mn was experimentally studied by thermal diffusivity measurements in close vicinity of the Curie temperature. Because the inverse of the thermal diffusivity has the same critical behavior as the specific heat, this allowed us to determine the critical exponent α for the samples investigated. As the critical temperature was approached, the value of the critical exponent α, for most of the samples under investigation, showed a clear crossover from the mean-field-like to the Ising-like critical behavior. Investigation of this crossover behavior has enabled us to determine the values of the Ginzburg number and the exchange interaction length in Ga _1-xMn _xAs.