Femtosecond x-ray absorption spectroscopy of spin and orbital angular momentum in photoexcited Ni films during ultrafast demagnetization

TL;DR

This study uses femtosecond x-ray absorption spectroscopy to observe the ultrafast reduction of spin and orbital angular momentum in Ni films during demagnetization, highlighting the role of spin-orbit interactions.

Contribution

First direct measurement of spin and orbital angular momentum dynamics in Ni during ultrafast demagnetization using x-ray magnetic circular dichroism.

Findings

Both spin and orbital angular momentum decrease with a 130 fs time constant.

Spin-orbit interaction increases by 6% during demagnetization.

Demonstrates the importance of spin-orbit processes in ultrafast demagnetization.

Abstract

We follow for the first time the evolution of the spin and orbital angular momentum of a thin Ni film during ultrafast demagnetization, by means of x-ray magnetic circular dichroism. Both components decrease with a 130 +/- 40 fs time constant upon excitation with a femtosecond laser pulse. Additional x-ray absorption measurements reveal an increase in the spin-orbit interaction by 6 +/- 2 % during this process. This is the experimental demonstration quantifying the importance of spin-orbit mediated processes during the demagnetization.