The Multi-Scale Dynamics of All-Optical Exchange Bias Reversal

TL;DR

This paper investigates ultrafast laser-induced exchange bias reversal in ferromagnetic/antiferromagnetic thin films, combining experimental observations with a microscopic model to enable rapid, on-demand reprogramming of magnetic states for advanced device applications.

Contribution

It introduces a comprehensive microscopic framework that explains ultrafast exchange bias setting and reversal, guiding the design of optimized material stacks for reprogrammable magnetic devices.

Findings

Ultrafast laser pulses can reversibly set exchange bias without magnetic fields.

The developed model accurately describes femto- to millisecond scale dynamics.

Material and stack design insights improve reprogramming efficiency.

Abstract

Pinning magnetization in a ferromagnetic thin film is commonly realized through exchange biasing with an adjacent antiferromagnet. Field-cooling from above the N\'{e}el temperature is a reliable yet slow re-pinning method in exchange-biased systems. For on-demand reprogrammable devices, localized and rapid exchange bias repinning methods are essential. Recent work has shown that femtosecond laser pulses enable field-free reversal of exchange bias in tailored multilayer stacks. Contrary to field-cooling, our experiments with ultrafast excitation reach hitherto unexplored regimes in the exchange bias setting process. Here, we unravel these observations by considering both ultrafast magnetization dynamics on the femto- to picosecond timescale and slow heat-driven dynamics on millisecond timescales and upwards. We develop a microscopic framework of exchange bias setting in a polycrystalline antiferromagnetic thin film like IrMn that provides a complete description of the observations in our present experiments and those found in literature. We expand the use of our model by identifying material platforms and stack designs that lead to optimized performance, aiding further development of optically reprogrammable devices.