Phase transformations in the Mn-Ge system and in Ge$_x$Mn$_{1-x}$ diluted semiconductors

Results of an X-ray diffraction study as well as magnetic and electrical measurements of the solid-state reactions in Ge/Mn polycrystalline films of an 80/20 atomic composition have been presented. It has been shown that the ferromagnetic Mn$_5$Ge$_3$ phase is formed first on the Ge/Mn interface after annealing at $\sim 120\,^\circ$C. The further increase in the annealing temperature to $300\,^\circ$C leads to the beginning of the synthesis of the Mn$_{11}$Ge$_8$ phase, which becomes dominating at $400\,^\circ$C. The existence of new structural transitions in the Mn-Ge system in the region of $\sim\,120$ and $\sim\,300\,^\circ$C has been predicted on the basis of the presented results and results obtained earlier when studying solid-state reactions in different film structures. The supposition about the general chemical mechanisms of the synthesis of the Mn$_5$Ge$_3$ and Mn$_{11}$Ge$_8$ phases during the solid-state reactions in the Ge/Mn films of the 80/20 atomic composition and the phase separation in Ge$_x$Mn$_{1-x}$ ($x > 0.95$) diluted semiconductors has been substantiated.