Spin–orbit torque driven skyrmion nucleation in antiferromagnetic/ferromagnetic heterostructures: synergistic influence of polarization direction and antiferromagnetic anisotropy

The nucleation of magnetic skyrmions in Antiferromagnetic(AFM)/Ferromagnetic(FM) Heterostructures driven by spin--orbit torque (SOT) is investigated using micromagnetic simulations with an effective description of the AFM layer. By comparing uniaxial, perpendicular, and easy-plane AFM anisotropies under both in-plane and out-of-plane SOT polarizations, we identify two distinct nucleation modes: boundary-dominated and interior-dominated. We show that the SOT polarization direction determines whether interior nucleation can be activated, whereas the AFM anisotropy controls the current threshold by modulating the spatial distribution of the effective Ruderman--Kittel--Kasuya--Yosida (RKKY) torque. In particular, easy-plane anisotropy stabilizes a vortex-like AFM spin texture, which enhances the spatially distributed torque acting on the ferromagnetic layer and enables interior-dominated nucleation at reduced current densities. A continuous transition between the two modes is further demonstrated by tuning the spin-polarization direction. These results clarify the synergistic influence of SOT symmetry and AFM anisotropy and provide guidelines for low-power, field-free skyrmion generation.