Robust perpendicular exchange coupling in an ultrathin CoO/PtFe double layer: Strain and spin orientation

We report on the exchange coupling and magnetic properties of a strained ultrathin CoO/PtFe double layer with perpendicular magnetic anisotropy. The cobalt oxide growth by reactive molecular beam epitaxy on a Pt-terminated PtFe/Pt(001) surface gives rise to a hexagonal surface and a monoclinic distorted CoO 3 nm film at room temperature. This distorted ultrathin CoO layer couples with the PtFe(001) layer establishing a robust perpendicular exchange bias shift. Soft x-ray absorption spectroscopy provides a full description of the spin orientations in the CoO/PtFe double layer. The exchange bias shift is preserved up to the N\'eel antiferromagnetic ordering temperature of ${T}_{N}=293$ K. This unique example of selfsame value for blocking and ordering temperatures, yet identical to the bulk ordering temperature, is likely related to the original strain-induced distortion and strengthened interaction between the two well-ordered spin layers.