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 Fe 4 N are investigated in strained tetragonal Fe 4 N/BiFeO 3 (001) heterostructures with the Fe A Fe B /Fe–O 2 termination using the first-principles calculations. Different from the d 2 = d xz + d yz + d z 2 favored PMA in previously reported Fe film, for all the Fe 4 N atomic layers at the biaxial strain of S, all d orbitals (i.e., d 1 = d xy + d x 2 – y 2 and d 2 ) make contributions to the PMA at S = 0% and in-plane magnetic anisotropy (IMA) at S = −2 and 2%. Specifically, the d 1 –d 2 orbital oscillation preserves (or favors) the PMA in 0% strained Fe 4 N, where the stronger MAE contribution alternates between d 1 and d 2 in adjacent Fe 4 N layers. However, at S = −2 and 2%, the whole Fe 4 N shows IMA with stable d 1 and d 2 contributions. Moreover, the PMA in the unstrained Fe 4 N can be transformed into the IMA by a strain of −2% with a high spin polarization, where Fe 4 N/BiFeO 3 interfacial effects are crucial. The PMA preserved by the controllably orbital oscillation in highly spin-polarized Fe 4 N paves a way for developing novel spintronic devices.