Spin-flip processes and ultrafast magnetization dynamics in Co - unifying the microscopic and macroscopic view of femtosecond magnetism

TL;DR

This study investigates femtosecond magnetization dynamics in cobalt films using combined pump-probe techniques, revealing that Elliott-Yafet spin-flip processes drive ultrafast demagnetization, while electron-magnon excitation does not significantly affect overall magnetization.

Contribution

It unifies microscopic and macroscopic views of femtosecond magnetism by identifying key spin-flip mechanisms responsible for ultrafast demagnetization in cobalt.

Findings

Elliott-Yafet spin-flip processes are crucial for 300 fs demagnetization.

Electron-magnon excitation does not significantly impact overall magnetization.

Combined techniques enable microscopic understanding of ultrafast magnetization dynamics.

Abstract

The femtosecond magnetization dynamics of a thin cobalt film excited with ultrashort laser pulses has been studied using two complementary pump-probe techniques, namely spin-, energy- and time-resolved photoemission and time-resolved magneto-optical Kerr effect. Combining the two methods it is possible to identify the microscopic electron spin-flip mechanisms responsible for the ultrafast macroscopic magnetization dynamics of the cobalt film. In particular, we show that electron-magnon excitation does not affect the overall magnetization even though it is an efficient spin-flip channel on the sub-200 fs timescale. Instead we find experimental evidence for the relevance of Elliott-Yafet type spin-flip processes for the ultrafast demagnetization taking place on a time scale of 300 fs.