  Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer
and a ferromagnetic CoPt multilayer were examined to understand the effects of
different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the
magnetic electrodes, especially after annealing at 350 C. Loss of perpendicular
anisotropy in MRG is strongly correlated with a reduction in the
substrate-induced tetragonality due to relaxation of the crystal structure. Hf
and Mo are able to stabilise the crystal lattice by filling defects that would
be removed during annealing, maintaining the strain in the crystal. The
reduction in squareness of the MRG hysteresis loop measured by anomalous Hall
effect is <10 %, making it useful in active devices. The solubility of both Hf
and Mo in MRG is a source of additional valence electrons, which results in an
increase in compensation temperature Tcomp . Furthermore, a (1 1 0) texture in
the perpendicular Co/Pt free layer promoted by a Mo spacer layer is the only
one that retains its perpendicular anisotropy on annealing.
