Probing ultrafast changes of spin and charge density profiles with resonant XUV magnetic reflectivity at the free-electron laser FERMI.

C Gutt,U Pietsch,L Raimondi,H Zabel,M Kläui,G Jakob,E Pedersoli,F Capotondi,M Kiskinova,T Sant,I P Nikolov,D Ksenzov,S Jaiswal

doi:10.1063/1.4990650

Abstract

We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q-resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Qz, we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film.

Highlights

The prospect of controlling magnetization on ultrafast time scales is of considerable interest since the first observation of laser induced ultrafast demagnetization by Beaurepaire et al.1 It has opened up the opportunity for light-controlled ultrafast magnetic data storage that requires profound understanding of the physics of ultrafast spin-flip processes, ultrafast spin dependent transport processes, and the complex interaction of electrons, spin, and lattice degrees of freedom in condensed matter systems
We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI
We do not expect any fundamental obstacle for measuring high precision asymmetries at the L-edges, yielding a much higher spatial resolution

Summary

INTRODUCTION

The prospect of controlling magnetization on ultrafast time scales is of considerable interest since the first observation of laser induced ultrafast demagnetization by Beaurepaire et al. It has opened up the opportunity for light-controlled ultrafast magnetic data storage that requires profound understanding of the physics of ultrafast spin-flip processes, ultrafast spin dependent transport processes, and the complex interaction of electrons, spin, and lattice degrees of freedom in condensed matter systems. The prospect of controlling magnetization on ultrafast time scales is of considerable interest since the first observation of laser induced ultrafast demagnetization by Beaurepaire et al.1 It has opened up the opportunity for light-controlled ultrafast magnetic data storage that requires profound understanding of the physics of ultrafast spin-flip processes, ultrafast spin dependent transport processes, and the complex interaction of electrons, spin, and lattice degrees of freedom in condensed matter systems. The hot electrons may mediate spin-flip processes via coupling to the lattice system and they are capable of inducing further demagnetization by transporting energy away from the IR absorption region. In this way, a spatially inhomogeneous cloud of hot spins transverses through the sample with spin-density modulations on fs time and nm length scales. We report the first proof of principle ultrafast magnetic reflectivity experiment demonstrating the feasibility and the type of information that can be obtained from analyzing reflectivity results on the fs time scale

THEORY

EXPERIMENTAL

RESULTS AND DISCUSSION