Effect of the magnon dispersion on the longitudinal spin Seebeck effect in yttrium iron garnets

Abstract

We study the temperature dependence of the longitudinal spin-Seebeck effect (LSSE) in a yttrium iron garnet Y 3 Fe 5 O 12 (YIG) / Pt system for samples of different thicknesses. In this system, the thermal spin torque is magnon-driven. The LSSE signal peaks at a specific temperature that depends on the YIG sample thickness. We also observe freeze-out of the LSSE signal at high magnetic fields, which we attribute to the opening of an energy gap in the magnon dispersion. We observe partial freeze-out of the LSSE signal even at room temperature, where k B T is much larger than the gap. This suggests that a subset of the magnon population with an energy below k B T C (T C ∼ 40 K) contribute disproportionately to the LSSE; at temperatures above T C , we label these magnons subthermal magnons. The T-dependence of the LSSE at temperatures below the maximum is interpreted in terms of a new empirical model that ascribes most of the temperature dependence to that of the thermally driven magnon flux.2

Long-range pure magnon spin diffusion observed in a nonlocal spin-Seebeck geometry

“…As these spins are both generated and detected in the presence of Tz, Vy may contain contributions from both the longitudinal SSE [9] and the anomalous Nernst effect (ANE) [21,22] . A schematic of the local configuration is shown in Fig.…”

Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

“…26,27 This is supported by several recent experiments: the dependence of SSE voltage with the thickness of F, 28 the enhancement of the SSE voltage in magnetic multilayers, 29 and the suppression of the SSE at high magnetic fields. 30,31 The SSE has potential advantages over conventional thermoelectric technologies for thermal energy harvesting. The experimental geometry, having paths for heat and electric currents independent and perpendicular to each other, allows to have two different materials that can be optimised independently and it is also advantageous for the implementation of thin film devices over large surfaces, for example, simply by thin film coating.…”

Characteristic length scale of the magnon accumulation in Fe3O4/Pt bilayer structures by incoherent thermal excitation

“…8 Two length scales are involved in magnon transport: one related with inelastic scattering and accessible by thermal conductivity measurements; 9,10 the other one is associated with spin-flip scattering and relevant in experiments of SSE when varying the film thickness. 6,[11][12][13] The magnitude of the spin current injected in NM is determined by the magnon spin current in FM and the boundary conditions. The output voltage in the NM layer depends on both NM and FM layer thickness 5 opening the possibility to better understand the physical properties involved to optimize the SSE signal in order to increase the output power.…”