No abstract

No abstract

We have characterized the structural and magnetic properties of low-temperature molecular-beam epitaxy grown Ge: Mn by means of high-resolution transmission electron microscopy ͑HR-TEM͒, energy dispersive x-ray spectroscopy, and superconducting quantum interference device ͑SQUID͒ magnetometry. We find a coherent incorporation of Mn 5 Ge 3 clusters in an epitaxially grown Ge: Mn matrix, which shows the characteristics of a diluted magnetic semiconductor phase of Mn-doped Ge. The clusters are preferentially oriented with the hexagonal ͓0001͔ direction parallel to the ͓001͔ growth direction of the Ge: Mn matrix, as determined from both HR-TEM and SQUID measurements.

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−x Mn x , with freezing temperatures of T f = 12 K and T f = 15 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 Ge 0.96 Mn 0.04 , AC susceptibility measurements show a peak around T f , with the peak position T ′ f shifting as a function of the driving frequency f by ∆T ′ f /[T ′ f · ∆logf ] ≈ 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.