Spin-glass-like behavior of Ge:Mn

We present a detailed study of the magnetic properties of low-temperature molecular-beam-epitaxy-grown Ge:Mn dilute magnetic semiconductor films. We find strong indications for a frozen state of Ge_1-xMnₓ, with freezing temperatures of Tf=120.3em0exK and Tf=150.3em0exK for samples with $x=0.04$ and $x=0.2$, respectively, determined from the difference between field-cooled and zero-field-cooled magnetization. For Ge0.96Mn0.04, ac susceptibility measurements show a peak around Tf, with the peak position Tf^' shifting as a function of the driving frequency f by ${Δ}{T}f^{{'}}∕[{T}f^{{'}}{{0.2em}{0ex}}{Δ}{{0.2em}{0ex}}log{{0.2em}{0ex}}f]{≈}0.06$, whereas for sample ${Ge}0.8{Mn}0.2$ a more complicated behavior is observed. Furthermore, both samples exhibit relaxation effects of the magnetization after switching the magnitude of the external magnetic field below ${T}f$ which are in qualitative agreement with the field- and zero-field-cooled magnetization measurements. These findings consistently show that Ge:Mn exhibits a frozen magnetic state at low temperatures and that it is not a conventional ferromagnet.