  Frustrated magnets can host numerous exotic many-body quantum and topological
phenomena. GeNi$_2$O$_4$ is a three dimensional $S=1$ frustrated magnet with an
unusual two-stage transition to the two-dimensional antiferromagnetic ground
state, while GeCu$_2$O$_4$ is a high-pressure phase with a strongly
tetragonally elongated spinel structure and magnetic lattice formed by $S=1/2$
CuO$_2$ linear chains with frustrated exchange interactions and exotic magnetic
behavior. Here we report on the first thin-film epitaxial stabilization of
these two compounds. Developed growth mode, surface morphology, crystal
structure and copper valence state were characterized by in-situ reflection
high-energy electron diffraction, atomic force microscopy, X-ray reflectivity,
X-ray diffraction, X-ray photoelectron spectroscopy and resonant X-ray
absorption spectroscopy. Our results pave an alternative route to the
comprehensive investigation of the puzzling magnetic properties of these
compounds and exploration of novel emergent features driven by strain.
