Femtosecond spin voltage measurement helps pull spintronics into the ultrafast domain

Electronics use electric charges to process, store, and transfer information. Spintronics, which also use spin, may help produce high speed, low power computing devices.

Just as a voltage drives a current in electronics, a spin voltage, which is the difference between the chemical potentials of the two spin directions, drives a spin current in spintronics. Seeking to improve the ability to measure spin voltage on a fast timescale, Bühlmann et al. present a method for doing so on the femtosecond timescale.

Ultrafast demagnetization can produce femtosecond spin current pulses. After performing ultrafast demagnetization in a thin iron film, the authors used spin- and time-resolved photoelectron spectroscopy to observe a shift in the spin-dependent Fermi edge, which corresponds to the chemical potential. The difference between the shifted chemical potential of one spin direction compared to the other spin direction produced a spin voltage with a value of 50 mV, which matches theoretical predictions. The spin voltage pulse lasted about 100 fs.

The ability to generate and measure femtosecond spin currents could help further understanding of fast processes in spintronics. The authors also hope that their work can help provide a visual aid for a more complete theory that describes the onset of spin current pulses following ultrafast demagnetization.

“Seeing a shift of the chemical potentials of spin voltage leads us to a simpler physical picture of this process,” said author Yves Acremann. “We can use simple thermodynamics to approximately describe the generation of a spin current pulse.”

Source: “Detection of femtosecond spin voltage pulses in a thin iron film,” by K. Bühlmann, G. Saerens, A. Vaterlaus, and Y. Acremann, Structural Dynamics (2020). The article can be accessed at https://doi.org/10.1063/4.0000037 .