Measuring the atomic spin-flip scattering rate by x-ray emission spectroscopy

Area of Science:

• Condensed Matter Physics
• Materials Science
• Ultrafast Magnetism

Background:

• Demagnetization dynamics after ultrafast laser pulses are extensively studied, but microscopic mechanisms remain underexplored.
• Electron-phonon scattering-induced spin-flip of conduction electrons is a key demagnetization mechanism in transition metal ferromagnets.

Purpose of the Study:

• To experimentally monitor the electron-phonon mediated spin-flip scattering rate in nickel.
• To investigate the role of spin-flip scattering in ultrafast demagnetization.

Main Methods:

• Utilized x-ray emission spectroscopy (XES) leveraging atomic symmetry selection rules.
• Monitored the intensity of the 3d → 2p_3/2 decay peak as a function of phonon population.
• Compared results in nickel with a diamagnetic control sample, copper.

Main Results:

• Observed a decrease in the 3d → 2p_3/2 decay peak intensity with increasing phonon population in nickel.
• This intensity waning indicates an increased angular momentum transfer scattering rate due to spin-flip.
• Determined a spin relaxation time scale of approximately 50 femtoseconds in nickel's 3d-band at room temperature.
• No similar peak evolution was observed in copper, confirming the phenomenon's magnetic origin.

Conclusions:

• Electron-phonon scattering significantly contributes to spin-flip processes in nickel's ultrafast demagnetization.
• X-ray emission spectroscopy provides a sensitive method to probe spin-flip scattering rates.
• The findings offer crucial insights into the microscopic mechanisms governing demagnetization in ferromagnetic materials.