Perpendicular Magnetic Anisotropy Preserved by Orbital Oscillation in Strained Tetragonal Fe4N/BiFeO3 Bilayers.

Orbital performances are important for inducing and manipulating the perpendicular magnetic anisotropy (PMA) in spintronic devices. Herewith, the orbital-mediated PMA in highly spin-polarized Fe4N are investigated in strained tetragonal Fe4N/BiFeO3(001) heterostructures with the FeAFeB/Fe-O2 termination using the first-principles calculations. Different from the d2 = dxz + dyz + dz2 favored PMA in previously reported Fe film, for all the Fe4N atomic layers at the biaxial strain of S, all d orbitals (i.e., d1 = dxy + dx2-y2 and d2) make contributions to the PMA at S = 0% and in-plane magnetic anisotropy (IMA) at S = -2 and 2%. Specifically, the d1-d2 orbital oscillation preserves (or favors) the PMA in 0% strained Fe4N, where the stronger MAE contribution alternates between d1 and d2 in adjacent Fe4N layers. However, at S = -2 and 2%, the whole Fe4N shows IMA with stable d1 and d2 contributions. Moreover, the PMA in the unstrained Fe4N can be transformed into the IMA by a strain of -2% with a high spin polarization, where Fe4N/BiFeO3 interfacial effects are crucial. The PMA preserved by the controllably orbital oscillation in highly spin-polarized Fe4N paves a way for developing novel spintronic devices.