Spin Hall voltages from a.c. and d.c. spin currents.

Dahai Wei,Mirko Ribow,Georg Woltersdorf,Christian H Back,Martin Obstbaum

doi:10.1038/ncomms4768

Abstract

In spin electronics, the spin degree of freedom is used to transmit and store information. To this end the ability to create pure spin currents—that is, without net charge transfer—is essential. When the magnetization vector in a ferromagnet–normal metal junction is excited, the spin pumping effect leads to the injection of pure spin currents into the normal metal. The polarization of this spin current is time-dependent and contains a very small d.c. component. Here we show that the large a.c. component of the spin currents can be detected efficiently using the inverse spin Hall effect. The observed a.c.-inverse spin Hall voltages are one order of magnitude larger than the conventional d.c.-inverse spin Hall voltages measured on the same device. Our results demonstrate that ferromagnet–normal metal junctions are efficient sources of pure spin currents in the gigahertz frequency range.

Highlights

In spin electronics, the spin degree of freedom is used to transmit and store information
When the magnetization vector in a ferromagnet (FM)–normal metal (NM) junction is excited at ferromagnetic resonance (FMR), spin pumping leads to the injection of pure spin currents in the NM
We demonstrate experimentally the presence of a large a.c. component in the inverse spin Hall effect (ISHE) voltage signal in NM/FM bilayers, where the a.c. spin current is generated by spin pumping at FMR

Summary

Introduction

The spin degree of freedom is used to transmit and store information. When the magnetization vector in a ferromagnet–normal metal junction is excited, the spin pumping effect leads to the injection of pure spin currents into the normal metal The polarization of this spin current is time-dependent and contains a very small d.c. component. When the magnetization vector in a ferromagnet (FM)–normal metal (NM) junction is excited at ferromagnetic resonance (FMR), spin pumping leads to the injection of pure spin currents in the NM D.c. voltage signals in ferromagnetic insulator/ferromagnetic conductor bilayers have been interpreted as spin rectification in the ferromagnetic conductor material[14] These experiments provide strong evidence for the presence of a large a.c. component of the spin current generated by spin pumping. Our results demonstrate that FM–NM junctions are very efficient sources of pure spin currents in the GHz frequency range and we believe that our result will stimulate the development of a.c. spintronics[18,19]

Methods

Results

Conclusion