Engineering Field-Like Spin Torques with Sign Reversal Using a Fe ₃ GeTe ₂ Insertion Layer

Current-induced spin–orbit torque (SOT) provides an efficient electrical approach to manipulate magnetization in spintronic devices, where most research has focused on the enhancement of damping-like (DL)-SOT. However, field-like (FL)-SOT, which has been proven to dominate ultrafast (subnanosecond) in-plane magnetization manipulation, has received relatively little attention. Here, we demonstrate robust FL-SOT modulation, even with sign reversal, by engineering SOT-material/ferromagnet interfaces in typical Pt/CoFeB SOT bilayers through an Fe3GeTe2 insertion layer. Our results indicate that FL-SOT can be modulated by a factor of 2 with sign reversal, while DL-SOT is also modulated but consistently retains the same sign. Furthermore, control samples with an additional Cu insertion layer confirm that the independent modulation and sign reversal of FL-SOT are determined by the proximity-induced interfacial ferromagnetism via the Fe3GeTe2 insertion layer, which alters spin scattering at the Pt/CoFeB interfaces. This work provides an effective pathway for precisely tailoring the often-neglected FL-SOT, which is crucial for developing ultrafast SOT devices.