  We report on the first integration of an antiferromagnetic Heusler compound
acting as a pinning layer into magnetic tunneling junctions. The
antiferromagnet Ru$_2$MnGe is used to pin the magnetization direction of a
ferromagnetic Fe layer in MgO based thin film tunnelling magnetoresistance
stacks. The samples were prepared using magnetron co-sputtering. We investigate
the structural properties by X-ray diffraction and reflection, as well as
atomic force and high-resolution transmission electron microscopy. We find an
excellent crystal growth quality with low interface roughnesses of 1-3 \r{A},
which is crucial for the preparation of working tunnelling barriers. Using Fe
as a ferromagnetic electrode material we prepared magnetic tunneling junctions
and measured the magnetoresistance. We find a sizeable maximum
magnetoresistance value of 135%, which is comparable to other common Fe based
MTJ systems.
