Percolation ferromagnetism and spin waves in Ge:Mn thin films

Abstract

We studied magnetic properties of thin Ge:Mn films obtained by implantation of ${\text{Mn}}^{+}$ ions into a single crystalline bulk germanium. In the net magnetic moment we were able to separate contributions originating from dispersed ${\text{Mn}}^{2+}$ ions, ferromagnetic ${\text{Mn}}_{5}{\text{Ge}}_{3}$ precipitates, and regions of the germanium matrix enriched with diluted manganese---${\text{Mn}}_{\text{m}}{\text{Ge}}_{\text{n}}$ alloys. In the subsystem of dispersed ${\text{Mn}}^{2+}$ ions we observed a percolation transition into the ferromagnetic state at $T\ensuremath{\le}13\text{ }\text{K}$. Collective excitations, standing spin waves, were also detected below this temperature. The main parameters of the exchange interaction obtained from the analysis of the experimental spin-wave resonance data are consistent with results acquired from static magnetic measurements as well as with theoretical estimations for a percolation ferromagnet. Thus, we demonstrate that low-temperature magnetic properties of group IV magnetic semiconductor can be successfully explained within a magnetic polaron model.