Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons

Shan, Juan; Cornelissen, Ludo J.; Vlietstra, N.; Youssef, J. Ben; Kuschel, Timo; Duine, R. A.; Wees, B. J. van

doi:10.1103/physrevb.94.174437

Cited by 95 publications

(168 citation statements)

References 49 publications

Supporting

Mentioning

139

Contrasting

Order By: Relevance

“…A model for thermal generation of magnon spin currents based on the bulk SSE 42 which takes into account a non-zero magnon chemical potential has been proposed in order to explain the observations 34 . This model has been reasonably successful in explaining the nonlocal signals (due to both thermal and electrical generation) in the long distance limit 23,33 , yet is not fully consistent with experiments in the short distance limit for thermally generated magnons 33 . The model is explained in detail in Refs.…”

Section: Modellingmentioning

confidence: 90%

See 1 more Smart Citation

Nonlocal magnon-polaron transport in yttrium iron garnet

et al. 2017

View full text Add to dashboard Cite

The spin Seebeck effect (SSE) is observed in magnetic insulator|heavy metal bilayers as an inverse spin Hall effect voltage under a temperature gradient. The SSE can be detected nonlocally as well, viz. in terms of the voltage in a second metallic contact (detector) on the magnetic film, spatially separated from the first contact that is used to apply the temperature bias (injector). Magnon-polarons are hybridized lattice and spin waves in magnetic materials, generated by the magnetoelastic interaction. Kikkawa et al. [Phys. Rev. Lett. 117, 207203 (2016)] interpreted a resonant enhancement of the local SSE in yttrium iron garnet (YIG) as a function of the magnetic field in terms of magnon-polaron formation. Here we report the observation of magnon-polarons in nonlocal magnon spin injection/detection devices for various injector-detector spacings and sample temperatures. Unexpectedly, we find that the magnon-polaron resonances can suppress rather than enhance the nonlocal SSE. Using finite element modelling we explain our observations as a competition between the SSE and spin diffusion in YIG. These results give unprecedented insights into the magnon-phonon interaction in a key magnetic material.When sound travels through a magnet the local distortions of the lattice exert torques on the magnetic order due to the magnetoelastic coupling 1 . By reciprocity, spin waves in a magnet affect the lattice dynamics. The coupling between spin and lattice waves (magnons and phonons) has been intensively researched in the last half century 2,3 . Yttrium iron garnet (YIG) has been a singularly useful material here, because it can be grown with exceptional magnetic and acoustic quality 2 . Magnons and phonons hybridize at the (anti)crossing of their dispersion relations, a regime that has attracted recent attention [4][5][6][7][8][9][10] . When the quasiparticle lifetimebroadening is smaller than the interaction strength, the strong coupling regime is reached; the resulting fully mixed quasiparticles have been referred to as magnonpolarons 6,7 .In spite of the long history and ubiquity of the magnonphonon interaction, it still leads to surprises. Evidence of a sizeable magnetoelastic coupling in YIG was recently found in experiments on spin caloritronic effects, i.e. the spin Peltier 11 and spin Seebeck effect 12,13 (SPE and SSE respectively). Recently, Kikkawa et al. showed that the hybridization of magnons and phonons can lead to a resonant enhancement of the local SSE in YIG 9 . Bozhko et al. found that this hybridization can play a role in the thermalization of parametrically excited magnons using Brillouin light scattering. They observed an accumulation of magnon-polarons in the spectral region near the anticrossing between the magnon and transverse acoustic phonon modes 14 . However, these previous experiments did not address the transport properties of magnon-polarons.Nonlocal spin injection and detection experiments are of great importance in probing the transport of spin in metals 15 , semiconductors 16 and graphene 1...

show abstract

Section: Modellingmentioning

confidence: 90%

“…39. For the bulk spin Seebeck coefficient at zero field we use ζ 0 = 500 A/m, based on our previous work in which we gave an estimate for ζ at room temperature 33 . For GGG, the spin conductivity and spin Seebeck coefficient are set to zero.…”

Section: Methodsmentioning

confidence: 99%

Nonlocal magnon-polaron transport in yttrium iron garnet

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Additionally, phonon-magnon drag has been put into evidence in previous SSE experiments 8,9 , which, again, points to the importance of interactions between magnons and phonons. To the best of our knowledge, no explicit evidence for the effect of this length scale on SSE measurements has been reported to date.Previous articles on thin films using various growth techniques 10,11,12 have shown the SSE signal to increase with increasing YIG film thickness. In this study, we grow a series of 3 Pt|YIG|GGG heterostructures, with YIG thickness varying from 10 nm to 1 μm, using the same growth technique for all films.…”

mentioning

confidence: 94%

Evidence for the role of the magnon energy relaxation length in the spin Seebeck effect

et al. 2018

View full text Add to dashboard Cite

Temperature-dependent spin-Seebeck effect data on Pt|YIG (Y3Fe5O12)|GGG (Gd3Ga5O12) are reported for YIG films of various thicknesses. The effect is reported as a spin-Seebeck resistivity (SSR), the inverse spin-Hall field divided by the heat flux, to circumvent uncertainties about temperature gradients inside the films. The SSR is a non-monotonic function of YIG thickness. A diffusive model for magnon transport demonstrates how these data give evidence for the existence of two distinct length scales in thermal spin transport, a spin diffusion length and a magnon energy relaxation length. 2Since the discovery of the (longitudinal) spin-Seebeck effect (SSE) 1 , much work has been done to identify the length scales involved in the phenomenon. 2 Using nonlocal detection, it has been shown that relaxation of thermal magnons in YIG is governed by a spin diffusion length. 3The latter is reported to be around 10 μm, and, in some studies, increases to up to 70 μm at low temperatures. 4,5 . This has led to a consensus that the micron-scale dependence of SSE observed in planar geometries corresponds to the generation and accumulation of the nonequilibrium magnondensity gradients in the bulk. These experiments have been modeled theoretically in terms of magnon spin transport only, while assuming that the magnon-phonon processes leading to the relaxation of the magnon energy occur over very short length scales; hence, their effects can be disregarded. 3,5 Nevertheless, it is clear that magnon energy relaxation mechanisms by the phononic environment must be invoked generally for a complete understanding of thermal spin transport, and particularly for the physics underlying the SSE. Indeed, while heaters and thermometers couple to phonons, these must in turn couple to magnons in order to give rise to the SSE in a magnon-based system like YIG. These relaxation processes can be parameterized by the length over which magnon-to-phonon thermalization occurs, and the latter is expected to be a much smaller length scale than magnon spin-diffusion lengths; a theoretical argument can be found in Ref. [6]. Early work 7 defines an energy relaxation length similar to the one invoked here, but without quantifying it. Additionally, phonon-magnon drag has been put into evidence in previous SSE experiments 8,9 , which, again, points to the importance of interactions between magnons and phonons. To the best of our knowledge, no explicit evidence for the effect of this length scale on SSE measurements has been reported to date.Previous articles on thin films using various growth techniques 10,11,12 have shown the SSE signal to increase with increasing YIG film thickness. In this study, we grow a series of 3 Pt|YIG|GGG heterostructures, with YIG thickness varying from 10 nm to 1 μm, using the same growth technique for all films. We measure the temperature-dependent spin-Seebeck effect on these structures and of bulk single-crystal Pt|YIG. The spin-Seebeck signal increases for film thicknesses from 10 to 250 nm and again for the bulk Y...

show abstract

“…In addition to conventional spin pumping via microwave magnetic fields, [10][11][12] magnons in magnetic insulators (MIs) can be excited both electrically [13][14][15][16][17][18] and thermally. 13,19,20 The spin Hall effect is involved both in magnon generation and detection in electrically excited materials. [13][14][15][16][17][18] Moreover, practical progress in devices has utilized electrically excited magnons, 15 benefiting from previous transport property research in this topic.…”

mentioning

confidence: 99%

Lateral transport properties of thermally excited magnons in yttrium iron garnet films

Zhou

Shi

Han

et al. 2017

Applied Physics Letters

View full text Add to dashboard Cite

Spin information carried by magnons is attractive for computing technology and the development of magnon-based computing circuits is of great interest. However, magnon transport in insulators has been challenging, different from the clear physical picture for spin transport in conductors. Here we investigate the lateral transport properties of thermally excited magnons in yttrium iron garnet (YIG), a model magnetic insulator. Polarity reversals of detected spins in non-local geometry devices have been experimentally observed and are strongly dependent on temperature, YIG film thickness, and injector-detector separation distance. A competing two-channel transport model for thermally excited magnons is proposed, which is qualitatively consistent with the spin signal behavior. In addition to the fundamental significance for thermal magnon transport, our work furthers the development of magnonics by creating an easily accessible magnon source with controllable transport. a)

show abstract

Influence of yttrium iron garnet thickness and heater opacity on the nonlocal transport of electrically and thermally excited magnons

Cited by 95 publications

References 49 publications

Nonlocal magnon-polaron transport in yttrium iron garnet

Nonlocal magnon-polaron transport in yttrium iron garnet

Evidence for the role of the magnon energy relaxation length in the spin Seebeck effect

Lateral transport properties of thermally excited magnons in yttrium iron garnet films

Contact Info

Product

Resources

About