Enhanced ferromagnetic transition temperature induced by a microscopic structural rearrangement in the diluted magnetic semiconductor Ge$_{1-x}$Mn$_{x}$Te

摘要

The correlation between magnetic properties and microscopic structuralaspects in the diluted magnetic semiconductor Ge$_{1-x}$Mn$_{x}$Te isinvestigated by x-ray diffraction and magnetization as a function of the Mnconcentration $x$. The occurrence of high ferromagnetic-transition temperaturesin the rhombohedrally distorted phase of slowly-cooled Ge$_{1-x}$Mn$_{x}$Te isshown to be directly correlated with the formation and coexistence ofstrongly-distorted Mn-poor and weakly-distorted Mn-rich regions. It isdemonstrated that the weakly-distorted phase fraction is responsible for theoccurrence of high-transition temperatures in Ge$_{1-x}$Mn$_{x}$Te. When the Mnconcentration becomes larger, the Mn-rich regions start to switch into theundistorted cubic structure, and the transition temperature is suppressedconcurrently. By identifying suitable annealing conditions, we successfullyincreased the transition temperature to above 200 K for Mn concentrations closeto the cubic phase. Structural data indicate that the weakly-distorted phasefraction can be restored at the expense of the cubic regions upon theenhancement of the transition temperature, clearly establishing the direct linkbetween high-transition temperatures and the weakly-distorted Mn-rich phasefraction.