Spin caloric transport from density-functional theory

Popescu, Voicu; Kratzer, Peter; Entel, P.; Heiliger, Christian; Czerner, Michael; Tauber, Katarina; Töpler, Franziska; Herschbach, Christian; Fedorov, D. V.; Gradhand, Martin; Mertig, Ingrid; Kováčik, Roman; Mavropoulos, Phivos; Wortmann, Daniel; Blügel, Stefan; Freimuth, Frank; Mokrousov, Yuriy; Wimmer, Sebastian; Ködderitzsch, D.; Seemann, Marten; Chadova, Kristina; Ebert, H.

doi:10.1088/1361-6463/aae8c5

Cited by 17 publications

(12 citation statements)

References 244 publications

(612 reference statements)

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“…4(b) (black points), showing a finite magnitude even for T ≤ 100 K. This is also supported by experimental quantifications of S xx in bulk Pt [41] as well as thin films [42]. Considering that θ SN = S s yx /S xx (with S s yx the transverse Seebeck coefficient [43]), it follows that S s yx approaches zero at low temperatures, in accordance with theory [25,43,44]. This is based on the dominance of extrinsic contributions (i.e.…”

supporting

confidence: 78%

Low Temperature Suppression of the Spin Nernst Angle in Pt

Wimmer,

Gückelhorn,

Wimmer

et al. 2021

Preprint

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We demonstrate the low temperature suppression of the platinum (Pt) spin Nernst angle in bilayers consisting of the antiferromagnetic insulator hematite (α-Fe2O3) and Pt upon measuring the transverse spin Nernst magnetothermopower (TSNM). We show that the observed signal stems from the interplay between the interfacial spin accumulation in Pt originating from the spin Nernst effect and the orientation of the Néel vector of α-Fe2O3, rather than its net magnetization. Since the latter is negligible in an antiferromagnet, our device is superior to ferromagnetic structures, allowing to unambiguously distinguish the TSNM from thermally excited magnon transport (TMT), which usually dominates in ferri/ferromagnets due to their non-zero magnetization. Evaluating the temperature dependence of the effect, we observe a vanishing TSNM below ∼ 100 K. We compare these results with theoretical calculations of the temperature dependent spin Nernst conductivity and find excellent agreement. This provides evidence for a vanishing spin Nernst angle of Pt at low temperatures and the dominance of extrinsic contributions to the spin Nernst effect.

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confidence: 78%

Low Temperature Suppression of the Spin Nernst Angle in Pt

Wimmer,

Gückelhorn,

Wimmer

et al. 2021

Preprint

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“…(10). For a small electric field and a linearized Boltzmann equation, the vectorial mean free path Λ nk is obtained from [102] Λ nk = 1…”

Section: Discussionmentioning

confidence: 99%

Origin of the magnetic spin Hall effect: Spin current vorticity in the Fermi sea

Mook

Neumann

Johansson

et al. 2020

Phys. Rev. Research

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The interplay of spin-orbit coupling (SOC) and magnetism gives rise to a plethora of charge-to-spin conversion phenomena that harbor great potential for spintronics applications. In addition to the spin Hall effect, magnets may exhibit a magnetic spin Hall effect (MSHE), as was recently discovered [Kimata et al., Nature 565, 627-630 (2019)]. To date, the MSHE is still awaiting its intuitive explanation. Here we relate the MSHE to the vorticity of spin currents in the Fermi sea, which explains pictorially the origin of the MSHE. For all magnetic Laue groups that allow for nonzero spin current vorticities the related tensor elements of the MSH conductivity are given. Minimal requirements for the occurrence of a MSHE are compatibility with either a magnetization or a magnetic toroidal quadrupole. This finding implies in particular that the MSHE is expected in all ferromagnets with sufficiently large SOC. To substantiate our symmetry analysis, we present various models, in particular a two-dimensional magnetized Rashba electron gas, that corroborate an interpretation by means of spin current vortices. Considering thermally induced spin transport and the magnetic spin Nernst effect in magnetic insulators, which are brought about by magnons, our findings for electron transport can be carried over to the realm of spincaloritronics, heat-to-spin conversion, and energy harvesting. I. FROM THE CONVENTIONAL TO THE MAGNETIC SPIN HALL EFFECTThe spin Hall effect (SHE) [1] and its inverse are without doubt important discoveries [2][3][4][5][6] in the field of spintronics [7,8]. They serve not only as 'working horses' for generating and detecting spin currents [9] but also as key ingredients in spin-orbit torque devices for electric magnetization switching [10][11][12]. Compared to spin-transfer torque devices [13-17], spin-orbit torque devices are faster, more robust, and consume less power upon operation [18][19][20]; for a recent review see Ref. 21. While the anomalous Hall effect (AHE) in a magnet [22] produces a transverse charge current density upon applying an electric field E, the SHE in a nonmagnet produces a transverse spin current density j γ = σ γ E (γ = x, y, z indicates the transported spin component). Mathematically, the SHE is quantified by the antisymmetric part of the spin conductivity tensor σ γ . For example, the σ z xy element comprises z-polarized spin currents in x direction as a response to an electric field in y direction.In a simple picture, the intrinsic SHE [23,24] is explained by spinning electrons that experience a spin-dependent Magnus force caused by spin-orbit coupling (SOC). It appears as if 'built-in' spin-dependent magnetic fields evoke spin-dependent Lorentz forces that result in a transverse pure spin current. The extrinsic SHE [25][26][27] is covered by Mott scattering at defects [28].Since the SHE does not rely on broken time-reversal symmetry (TRS), it is featured in nonmagnetic metals [29] or semiconductors [2]. Imposing few demands on a material's properties, a SHE can be expected in...

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“…Over the last 20 years, in addition to thermoelectricity, much research on solid‐state thermal energy harvesting ( Figure 2 ) has also focused on thermionics and thermophotovoltaics . Researchers have also investigated new frontiers in spin‐caloritronics, spin‐Seebeck, and anomalous Nernst effects . However, with the rapid development of caloric (ferroic) materials and technologies for refrigeration and air conditioning, caloric (ferroic) power generation is being revisited and prototype devices are being developed.…”

Section: Introductionmentioning

confidence: 99%

Energy Applications of Magnetocaloric Materials

Kitanovski

2020

Advanced Energy Materials

362

156

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The need for energy‐efficient and environmentally friendly refrigeration, heat pumping, air conditioning, and thermal energy harvesting systems is currently more urgent than ever. Magnetocaloric energy conversion is among the best available alternatives for achieving these technological goals and has been the subject of substantial basic and applied research over the last two decades. The subject is strongly interdisciplinary, requiring proper understanding and efficient integration of knowledge in different specialized fields. This review article presents a historical and up‐to‐date account of the energy‐related applications of magnetocaloric materials and information about their processing and magnetic fields, thermodynamics, heat transfer, and other relevant characteristics. The article also discusses the conceptual design of magnetocaloric refrigeration and power generation systems and some guidelines for future research in the field.

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Spin caloric transport from density-functional theory

Cited by 17 publications

References 244 publications

Low Temperature Suppression of the Spin Nernst Angle in Pt

Low Temperature Suppression of the Spin Nernst Angle in Pt

Origin of the magnetic spin Hall effect: Spin current vorticity in the Fermi sea

Energy Applications of Magnetocaloric Materials

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