Understanding Field-Free Single-Shot Laser-Induced Reversal of Exchange Bias

Exchange bias is applied ubiquitously throughout the spintronics industry for pinning magnetic moment in an orientation robust against external magnetic field disturbances. Enabling efficient manipulation of the exchange-biased pinning direction is key to add or advance device functionality. Conventional methods for achieving this reorientation commonly require long heating times and assisting magnetic fields, thus limiting speed and versatility. Here, we demonstrate a field-free $180^\circ$ reorientation of perpendicular exchange bias in a thin film system integrating Co/Gd layers with IrMn. Single femtosecond laser pulses trigger a reversal of the pinning direction, while preserving the unidirectionality required for referencing. We formulate a theoretical microscopic framework involving a wide range of timescales that accurately reproduces the experimental outcomes. The understanding of the underlying mechanisms delivers guiding principles for designing reprogrammable spintronic devices.