Title: Enhanced ferromagnetic transition temperature induced by a microscopic structural rearrangement in the diluted magnetic semiconductor Ge$_{1-x}$Mn$_{x}$Te,
Abstract: The correlation between magnetic properties and microscopic structural
aspects in the diluted magnetic semiconductor Ge$_{1-x}$Mn$_{x}$Te is
investigated by x-ray diffraction and magnetization as a function of the Mn
concentration $x$. The occurrence of high ferromagnetic-transition temperatures
in the rhombohedrally distorted phase of slowly-cooled Ge$_{1-x}$Mn$_{x}$Te is
shown to be directly correlated with the formation and coexistence of
strongly-distorted Mn-poor and weakly-distorted Mn-rich regions. It is
demonstrated that the weakly-distorted phase fraction is responsible for the
occurrence of high-transition temperatures in Ge$_{1-x}$Mn$_{x}$Te. When the Mn
concentration becomes larger, the Mn-rich regions start to switch into the
undistorted cubic structure, and the transition temperature is suppressed
concurrently. By identifying suitable annealing conditions, we successfully
increased the transition temperature to above 200 K for Mn concentrations close
to the cubic phase. Structural data indicate that the weakly-distorted phase
fraction can be restored at the expense of the cubic regions upon the
enhancement of the transition temperature, clearly establishing the direct link
between high-transition temperatures and the weakly-distorted Mn-rich phase
fraction.