Joint perpendicular anisotropy and strong interlayer exchange coupling in systems with thin vanadium spacers

We study the influence of the insertion of a vanadium spacer layer between an FeCoB layer and a [Co/Ni] multilayer in an MgO substrate-based system mimicking the reference system of a perpendicular anisotropy magnetic tunnel junction. The anisotropy of the [Co/Ni] multilayer gradually improves with the vanadium thicknesses t, up to an optimized state for t = 8 Å, with little influence of the thermal annealing. The interlayer exchange coupling is ferromagnetic and very strong for t≤6 Å. It can be adjusted by thermal treatment at t = 8 Å from no coupling in the as-grown state to more than 2 mJ/m2 after 250 °C annealing. For this spacer thickness, the magnetic properties are consistent with the occurrence of a bcc (001) to an fcc (111) crystalline structure transition at the vanadium spacer. The remaining interlayer exchange coupling at t = 8 Å is still substantially higher than the one formerly obtained with a Tantalum spacer, which holds promise for further optimization of the reference layers of tunnel junctions meant for magnetic random access memories.