Detection of femtosecond spin injection into a thin gold layer by time and spin resolved photoemission

K Bühlmann,G Saerens,Y Acremann,A Vaterlaus

doi:10.1038/s41598-020-69477-y

Abstract

The ultrafast demagnetization effect allows for the generation of femtosecond spin current pulses, which is expected to extend the fields of spin transport and spintronics to the femtosecond time domain. Thus far, directly observing the spin polarization induced by spin injection on the femtosecond time scale has not been possible. Herein, we present time- and spin-resolved photoemission results of spin injection from a laser-excited ferromagnet into a thin gold layer. The injected spin polarization is aligned along the magnetization direction of the underlying ferromagnet. Its decay time depends on the thickness of the gold layer, indicating that transport as well as storage of spins are relevant. This capacitive aspect of spin transport may limit the speed of future spintronic devices.

Highlights

The ultrafast demagnetization effect allows for the generation of femtosecond spin current pulses, which is expected to extend the fields of spin transport and spintronics to the femtosecond time domain
If we investigate its behavior by studying the direct current (DC) transport characteristics the circuit will look as if it only consisted of resistors: At a frequency of 0 Hz, there is no current flowing through the terminals of the capacitors and the voltage drop across coils is zero
In this paper we discuss the capacitive aspect of spin transport in a thin gold layer and experimentally detect the injection and storage of spins with femtosecond time resolution

Summary

Introduction

The ultrafast demagnetization effect allows for the generation of femtosecond spin current pulses, which is expected to extend the fields of spin transport and spintronics to the femtosecond time domain. Its decay time depends on the thickness of the gold layer, indicating that transport as well as storage of spins are relevant. In this paper we discuss the capacitive aspect of spin transport in a thin gold layer and experimentally detect the injection and storage of spins with femtosecond time resolution. The spin currents are generated by the ultrafast demagnetization of a ferromagnet[12]: a ferromagnet is exposed to a femtosecond laser pulse; if the ferromagnet is in contact with a nonmagnetic metal, a spin current is injected into the non-magnet[13,14,15] Another way of generating femtosecond spin current pulses is by optical pumping of a heavy metal with circularly polarized light[16]

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Conclusion