Elsevier

Solid State Physics

Volume 64, 2013, Pages 123-156
Solid State Physics

Chapter Five - Spin Pumping and Spin Currents in Magnetic Insulators

https://doi.org/10.1016/B978-0-12-408130-7.00005-8Get rights and content

Abstract

This chapter is devoted to pure spin current transport across ferromagnet/normal metal (F/N) interfaces. It particularly focuses on the spin-pumping process, in which the magnetization dynamics excited in a ferromagnet result in a spin current across the interface, into an adjacent normal metal layer. Taking advantage of the spin-mixing conductance concept, we quantitatively analyze spin-pumping experiments in both metallic F/N as well as insulating F/N hybrid structures, and compare spin-pumping measurements based on the spin current-induced modification of magnetization damping with the electrical detection of spin pumping via the inverse spin Hall effect. We furthermore compare spin-pumping experiments with other spin current generation schemes, namely the spin Seebeck effect and the spin Hall magnetoresistance, and show that all three effects can be quantitatively and consistently understood based on the spin-mixing conductance concept.

Section snippets

From Charge to Spin Currents

Charge and spin transport in electrical conductors are connected because of spin–orbit interaction (SOI) [1], [2], [5], [6], [7], [8]. In other words, in materials with finite spin–orbit coupling, a charge current will be accompanied by a spin current, and vice versa. In the literature, the term spin Hall effect (SHE) is now commonly used for the generation of a spin current from a charge current via spin–orbit coupling, while the expression inverse spin Hall effect (ISHE) refers to the

Spin Currents and Magnetization Damping

In this section, we address the effect of spin pumping on the magnetization dynamics in the ferromagnetic layer. In particular, we will focus on Gilbert damping in metallic and insulating ferromagnetic materials, since spin current transfer across the F/N interface in F/N heterostructures enhances this type of damping. The efficiency of this interlayer spin current transfer is thereby governed by the interfacial spin-mixing conductance. Accordingly, measurements of the magnetization damping in

Electrical Detection of Spin Currents Generated via Spin Pumping

In Section 2, we have seen that spin currents arising from resonant magnetization dynamics provide an additional damping channel for the magnetization in F/N heterostructures. This allows to infer the magnitude of the spin current, and to quantify the spin-mixing conductance g↑↓ from broadband FMR experiments (c.f. Table 5.1). A complimentary, second approach to quantify the spin currents in F/N hybrids exploits the ISHE in the normal metal layer. In this scheme, the net spin current is

Spin Currents and the Spin-Mixing Conductance Concept

Spin currents are not only important for spin pumping; rather, the generation and detection of spin currents are of key importance also for the spin Seebeck effect (SSE) [14], [15], [105], [106] and the SMR [73], [74], [75], [76], [77] in ferromagnetic insulator/normal metal hybrid systems. Each of these effects has been studied extensively in its own respect. However, spin pumping, SSE, and SMR are all governed by one and the same interface parameter: the spin-mixing conductance g↑↓. The

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