Spin Seebeck effect at microwave frequencies

Abstract

We experimentally study the transient voltage response of yttrium iron garnet/platinum bilayer samples subject to periodic heating up to gigahertz frequencies. We observe an intrinsic cutoff frequency of the induced thermopower voltage, which characteristically depends on the thickness of the yttrium iron garnet film. The cutoff frequency reaches values of up to 350 MHz in a 50 nm thick yttrium iron garnet film, but drops to below 1 MHz for several-micrometer-thick films. These data corroborate the notion that the magnon spectrum responsible for the spin current emission in the spin Seebeck effect can be shaped by tuning the thickness of the ferromagnetic layer.

Enhancement of the Spin Pumping Effect by Magnon Confluence Process in YIG/Pt Bilayers

“…In work we demonstrate a complex behavior of the thermal gradients in the YIG layer as a function of time and distance to the YIG/Pt interface under heating by similar microwave technique. This gradient generates a spin current due to the longitudinal spin Seebeck effect (LSSE) . As opposed to the spin pumping from parametric magnons, the thermally induced spin current flows from Pt to YIG that results in the opposite polarity of the generated voltage.…”

Picosecond Spin Seebeck Effect

“…To date, time-resolved ISHE-based LSSE measurements have achieved a time-resolution of the order of 1-100 nanoseconds [27,28]. Agrawal et al investigate micrometer-thick YIG layers and report that the time scale of the LSSE is determined by the rise-time of the temperature gradient in the YIG layer (∼300 ns).…”

“…Based on this interpretation, they estimate a magnon spin diffusion length of ∼500 nm for thermally excited magnons. Schreier et al investigate YIG layers with thicknesses between 50 nm and 30 µm applying heating frequencies up to ∼1 GHz [28].…”

One dimensional Cherenkov processes in ferromagnetic insulator

“…Recently, several experiments with the setup of YIG/Pt thin film bilayers have been launched to clarify this problem. It is shown that the cutoff frequency of microwaves to generate spin injection by spin Seebeck effect is up to 30MHz 16 or 6.875GHz 17 , depending on the thickness of the YIG film. The mean free path, the characteristic frequency and the relaxation time have been analyzed theoretically as well [18][19][20] .…”