  Perpendicular heterostructures based on a ferrimagnetic Mn2RuxGa (MRG) layer
and a ferromagnetic Co/Pt multilayer were examined to understand the effects of
different spacer layers (V, Mo, Hf, HfOx and TiN) on the interfaces with the
magnetic electrodes, 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. In the absence of
diffusion, strain and chemical ordering within MRG are correlated. The limited
solubility of both Hf and Mo in MRG is a source of additional valence
electrons, which results in an increase in compensation temperature Tcomp. This
also stabilises perpendicular anisotropy, compensating for changes in strain
and defect density. The reduction in squareness of the MRG hysteresis loop
measured by anomalous Hall effect is <10 %, making it useful in active devices.
Furthermore, a CoPt3 phase with (2 2 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.
