Abstract
We report the growth of Co-doped Ge
(
Co
x
Ge
1
−
x
)
thin films by low-temperature molecular-beam epitaxy and the ferromagnetic properties without any additional carrier doping. The as-grown
Co
0.02
Ge
0.98
has a Curie temperature,
T
C
∼
15
K
, while those
Co
x
Ge
1
−
x
with
x
⩾
4.0
at.
%
are ferromagnetic above room temperature. On the other hand,
Co
0.02
Ge
0.98
exhibit ferromagnetic ordering up to
T
C
∼
150
±
10
K
after a low-temperature annealing. A redshift in the Raman Ge-Ge mode was observed, indicating the substitution of Ge with Co atoms. The measured
Co
0.02
Ge
0.98
are of
p
type and exhibit pronounced anomalous Hall effects.