Exploring Co, Fe, and Ni Reference Layers for Single‐Pulse All‐Optical Reversal in Ferromagnetic Spin Valves

We investigate the magnetization reversal process induced by a single femtosecond laser pulse in ferromagnetic spin valves by systematically comparing reference layers composed of pure Co, Ni, and Fe. To circumvent the loss of perpendicular magnetic anisotropy associated with changes in reference layer material and thickness, we design spin valves with in-plane magnetizations. While antiparallel-to-parallel switching is observed for all three elements, parallel-to-antiparallel switching occurs only with a Co reference layer and is absent with Ni and Fe. This difference is attributed to the distinct ultrafast magnetization dynamics of the reference materials. Our results support the hypothesis that parallel-to-antiparallel switching requires a rapid remagnetization of the reference layer, which generates a substantial negative spin current polarized opposite to the free layer magnetization-an essential condition for triggering its reversal.