Ferromagnetism in Mn-implanted Ge and epitaxial GeC

20 keV energy Mn ions were implanted in two samples: 1) bulk Ge (100) and 2) a 250 nm thick epitaxial GeC film, grown on a Si (100) wafer. The GeC thin film was grown by UHV chemical vapor deposition using a mixture of germane (GeH$_4$) and methylgermane (CH$_3$GeH$_3$) gases and contains less than 1\% carbon. X-ray diffraction data shows a single crystal phase for the GeC film, and the surface rms roughness is about 0.3 nm, measured with AFM. The Mn implant dose was $1.1\times10^{16}$/cm$^2$ at a temperature of 300$^{\circ}$ C for both samples. For this relatively low energy Mn ion implant, the range is about 17 nm and the straggle is about 9 nm. A SQUID magnetometer study shows ferromagnetism in both samples. While the Curie temperature for both samples is about 180 K, the in-plane saturated magnetic moment per unit area for the first sample is about $2.2\times10^{-5}$emu/cm$^2$ and that for the second sample is about $3.0\times10^{-5}$emu/cm$^2$. These results show clear enhancement of magnetic properties of the Mn-implanted GeC thin film over the identically implanted Ge layer due to the presence of a small amount of carbon.