Laser-induced ultrafast demagnetization and perpendicular magnetic anisotropy reduction in a Co$_{88}$Tb$_{12}$ thin film with stripe domains

TL;DR

This study uses time-resolved x-ray scattering to investigate ultrafast demagnetization and magnetic anisotropy changes in a CoTb thin film, revealing domain wall broadening due to anisotropy reduction within a few picoseconds.

Contribution

It demonstrates that ultrafast laser pulses do not alter the spin texture immediately but induce domain wall broadening through anisotropy reduction after a few picoseconds.

Findings

No immediate change in spin texture within 1 ps

Domain wall broadening observed after 4 ps

Magnetic anisotropy decreases due to energy transfer to the lattice

Abstract

We use time-resolved x-ray resonant magnetic scattering (tr-XRMS) at the Co M$_{2,3}$- and Tb O$_1$-edges to study ultrafast demagnetization in an amorphous Co$_{88}$Tb$_{12}$ alloy with stripe domains. Combining the femtosecond temporal with nanometer spatial resolution of our experiment, we demonstrate that the equilibrium spin texture of the thin film remains unaltered by the optical pump-pulse on ultrashort timescales ($<$1 ps). However, after $\simeq$ 4 ps, we observe the onset of a significant domain wall broadening, which we attribute to a reduction of the uniaxial magnetic anisotropy of the system, due to energy transfer to the lattice. Static temperature dependent magnetometry measurements combined with analytical modeling of the magnetic structure of the thin film corroborate this interpretation.