Spin glass behaviour of amorphous Ge-Mn alloy thin films

Magnetic measurements are performed under ac and dc conditions on well characterized Ge_100-xMn_x (x in at.%) amorphous thin films prepared by thermal co-evaporation onto oxidized Si or glass substrates at room temperature. M-H hysteresis loops at 5K show that saturation does not occur even at a high applied field of 30 or 50kOe. The temperature dependence of the dc and ac susceptibility shows a cusp with a position and magnitude that vary with the frequency during the ac susceptibility measurements. These results suggest a spin glass behaviour at low temperatures. Two competing magnetic interactions between Mn ions, which are responsible for the spin glass behaviour, are considered to be the direct antiferromagnetic coupling and the indirect ferromagnetic coupling through conduction electrons or holes. Scaling analysis indicates that the indirect ferromagnetic interactions are long range.