Transient ferromagnetic state induced by ultrafast suppression of interlayer exchange coupling in synthetic antiferromagnets

The increasing demand for faster, denser, and low-power memory technologies has intensified interest in antiferromagnetic materials for ultrafast spintronic applications. Synthetic antiferromagnets, with tunable interlayer exchange coupling, provide a versatile platform for high-speed device engineering. Here, we investigate the ultrafast spin dynamics in a synthetic antiferromagnet using time-resolved magneto-optical Kerr effect measurements. We find that laser excitation leads to a significant, transient suppression of interlayer exchange coupling, with recovery occurring on a sub-nanosecond timescale. By combining density functional theory calculations with experimental analysis, we identify this suppression as arising from the demagnetization of adjacent ferromagnetic layers. The magnitude and orientation of atomic magnetic moments on either side of the spacer layer are shown to play a critical role in determining interlayer exchange coupling strength. These findings offer a new pathway for optically controlling the behavior of synthetic antiferromagnets and underscore the potential of interlayer exchange coupling engineering for next-generation memory and ultrafast spintronic devices.