Perpendicular magnetic anisotropy induced by NiMn-based antiferromagnetic films with in-plane spin orientations: Roles of interfacial and volume antiferromagnetic moments

Antiferromagnetic (AFM) thin films are promising materials for engineering the magnetic anisotropy of adjacent ferromagnetic (FM) films. In this work, we explored the effects of triggering perpendicular magnetic anisotropy (PMA) of FM films by applying a series of NiMn-based AFM films with in-plane-oriented spin structures. The vertically expanded face-centered tetragonal ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50}$ films alone could not induce PMA in Co/Ni films. By contrast, PMA was triggered through the application of Mn-rich NiMn alloy films or ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50}/1$-monolayer Mn $(\mathrm{Mn}/1\text{\ensuremath{-}}\mathrm{ML} {\mathrm{Ni}}_{50}{\mathrm{Mn}}_{50})$ heterostructures. Detailed analyses of a series of samples indicated that two criteria must be met for a NiMn-based AFM film to trigger PMA in a neighboring FM film: (1) perpendicular interface crystalline anisotropy of interfacial uncompensated Mn moments must be established, and (2) strengthened lateral exchange coupling to volume AFM moments must be made. This paper clarifies how NiMn-based AFM films with in-plane-oriented AFM spin structures trigger the PMA of FM films, thus identifying a pathway to increase control over antiferromagnet-induced PMA through the interface/volume magnetic engineering of AFM layers.