Large spin accumulation signals in ultrafast magneto-optical experiments

TL;DR

This paper demonstrates that ultrafast spin accumulations can produce magneto-optical signals comparable to or exceeding those from local magnetization, enabling new methods to probe spin transport in spintronics.

Contribution

It provides experimental evidence that spin accumulation signals in ultrafast magneto-optical experiments are larger than previously thought, challenging existing assumptions and offering new probing techniques.

Findings

Spin accumulation signals can be comparable or larger than local magnetization signals.

New framework for isolating and analyzing spin transport phenomena.

Potential for time and depth-resolved spin and orbital angular momentum measurements.

Abstract

Magneto-optical techniques have become essential tools in spintronics, enabling the investigation of spin dynamics in the ultrafast regime. A key challenge in this field has been to accurately isolate the contributions to magneto-optical signals of spin transport phenomena from the local magnetization dynamics. The contribution of transported and accumulated spins was long believed to be orders of magnitude smaller than that of the magnetization and thus previous approaches to disentangle these signals have relied on specific experimental designs, usually including thick metal layers. Here, we present experimental evidence demonstrating that the magneto-optical signal from ultrafast spin accumulations can, under certain conditions, be comparable to or even exceed that of the magnetic layer in a standard ultrafast demagnetization experiment. Our findings provide a new framework for accessing and isolating these spin accumulations, allowing for time and depth dependent probing of transported spin and/or orbital angular momentum.