Formation of ferromagnetic germanides by solid-state reactions in 20Ge/80Mn films

• Mn5Ge3 is an important compound for spintronic applications.
• Demonstration that Mn5Ge3 forms first phase at the Ge/Mn interface
• Influence C and O impurities on the magnetic properties Mn5Ge3 is discussed.
• Nature of the spinodal decomposition of the Ge-Mn solid solution is synthesis Mn5Ge3.

Solid state reactions between Ge and Mn films are systematically examined using X-ray diffraction, photoelectron spectroscopy, and magnetic and electrical measurements. The films have a nominal atomic ratio Ge:Mn = 20:80 and are investigated at temperatures from 50 to 500 ºC. It is established that after annealing at ~ 120 ºC, the ferromagnetic Mn5Ge3 phase is the first phase to form at the 20Ge/80Mn interface. As the annealing temperature increases to 300 ºC, the weak magnetic Mn5Ge2 + Mn3Ge phases simultaneously begin to grow and they become dominant at 400 ºC. Increasing the annealing temperature to 500 ºC leads to the formation of the ferromagnetic phase with a Curie temperature TC ~ 350–360 K and magnetization 14–25 kA/m at room temperature. The X-ray diffraction study of the samples shows the reflections from the Mn5Ge3 phase, and the photoelectron spectra contain the oxygen and carbon peaks. The homogeneous distribution of oxygen and carbon over the sample thickness suggests that the increased Curie temperature and magnetization are related to the migration of C and O atoms into the Mn5Ge3 lattice and the formation of the Nowotny phase Mn5Ge3СxOy.The initiation temperature (~ 120 °С) is the same in the Mn5Ge3 phase with the solid-state reactions in the Ge/Mn films as well as in the phase separation in the GexMn1 − x diluted semiconductors. Thus, we conclude that the synthesis of the Mn5Ge3 phase is the moving force for the spinodal decomposition of the GexMn1 − x diluted semiconductors.