Optical inter-site spin transfer probed by energy and spin-resolved transient absorption spectroscopy

Felix Willems,Sangeeta Sharma,Clemens Von Korff Schmising,Dieter W Engel,Stefan Eisebitt,J K Dewhurst,Daniel Schick,Peter Elliott,Christian Strüber

doi:10.1038/s41467-020-14691-5

Abstract

Optically driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. In the present work, we show that such an optical inter-site spin transfer (OISTR) from Pt to Co emerges as a dominant mechanism governing the ultrafast magnetization dynamics of a CoPt alloy. To demonstrate this, we perform a joint theoretical and experimental investigation to determine the transient changes of the helicity dependent absorption in the extreme ultraviolet spectral range. We show that the helicity dependent absorption is directly related to changes of the transient spin-split density of states, allowing us to link the origin of OISTR to the available minority states above the Fermi level. This makes OISTR a general phenomenon in optical manipulation of multi-component magnetic systems.

Highlights

Driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum
It was demonstrated that this technique gives access to the microscopic interplay of different elements in multi-component magnetic systems in a single measurement[24,25,26] and allows distinguishing laser-driven local and non-local magnetization dynamics[12,27] as well as exchange[28] and collective spin excitations[29,30]
Magnetic circular dichroism (MCD) in transmission geometry[19,25] can be explained by a simple two-step model[31]: absorption of circularly polarized photons in resonance with a core to valence state transition leads to spinpolarized photoelectrons via spin-orbit (SO) interaction

Summary

Introduction

Driven spin transport is the fastest and most efficient process to manipulate macroscopic magnetization as it does not rely on secondary mechanisms to dissipate angular momentum. We employ helicity dependent absorption spectroscopy around the M2,3 resonance of Co and compare the response of a pure Co film and a CoPt alloy to demonstrate that optical inter-site spin transfer (OISTR) between Pt and Co atoms in the two-component system CoPt dominates the early time dynamics leading to a more efficient and faster demagnetization.

Results

Conclusion