Optically excited spin pumping mediating collective magnetization dynamics in a spin valve structure

A P Danilov,D P Pattnaik,A W Rushforth,S A Cavill,M Bayer,B A Glavin,D R Yakovlev,A M Kalashnikova,C J Love,T L Linnik,A V Scherbakov,L A Shelukhin

doi:10.1103/physrevb.98.060406

Abstract

We demonstrate spin pumping, i.e. the generation of a pure spin current by precessing magnetization, without application of microwave radiation commonly used in spin pumping experiments. We use femtosecond laser pulses to simultaneously launch the magnetization precession in each of two ferromagnetic layers of a Galfenol-based spin valve and monitor the temporal evolution of the magnetizations. The spin currents generated by the precession cause a dynamic coupling of the two layers. This coupling has dissipative character and is especially efficient when the precession frequencies in the two layers are in resonance, where coupled modes with strongly different decay rates are formed.

Highlights

I.e., the generation of a pure spin current by precessing magnetization, without the application of microwave radiation commonly used in spin pumping experiments
In a spin valve structure consisting of two FM layers separated by a nonmagnetic spacer, the spin current generated by one layer drives the magnetization precession of the other layer [23,24,25,26]
At resonance, when the precession frequencies of the FM layers coincide, a coupled collective precessional mode forms [27,28,29]. This conventional approach has a drawback, : Applying monochromatic microwave fields for driving the magnetization precession lacks the flexibility required for nanoscale applications, it strictly sets the magnetization precession and spin current phase, and requires exact matching to the ferromagnetic resonance (FMR) frequency

Summary

Rapid Communications

At resonance, when the precession frequencies of the FM layers coincide, a coupled collective precessional mode forms [27,28,29] This conventional approach has a drawback, : Applying monochromatic microwave fields for driving the magnetization precession lacks the flexibility required for nanoscale applications, it strictly sets the magnetization precession and spin current phase, and requires exact matching to the FMR frequency. While laser pulses have been utilized for spin current generation via the transport of spin-polarized electrons from an optically excited magnetic region [32,33,34,35,36,37], evidence of pure spin currents generated by optically launched magnetization precession is lacking In this Rapid Communication, we report optically excited SP in a pseudospin valve (PSV) consisting of two FM layers separated by a normal metal spacer.

Laser pulse x

Mj d Mj dt