Spin-glass-like behavior of Ge:Mn

Abstract

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 ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}$, with freezing temperatures of ${T}_{f}=12\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${T}_{f}=15\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for samples with $x=0.04$ and $x=0.2$, respectively, determined from the difference between field-cooled and zero-field-cooled magnetization. For ${\mathrm{Ge}}_{0.96}{\mathrm{Mn}}_{0.04}$, ac susceptibility measurements show a peak around ${T}_{f}$, with the peak position ${T}_{f}^{\ensuremath{'}}$ shifting as a function of the driving frequency $f$ by $\ensuremath{\Delta}{T}_{f}^{\ensuremath{'}}∕[{T}_{f}^{\ensuremath{'}}\phantom{\rule{0.2em}{0ex}}\ensuremath{\Delta}\phantom{\rule{0.2em}{0ex}}\mathrm{log}\phantom{\rule{0.2em}{0ex}}f]\ensuremath{\approx}0.06$, whereas for sample ${\mathrm{Ge}}_{0.8}{\mathrm{Mn}}_{0.2}$ 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.