Theory of the spin Seebeck effect

Adachi, Hiroto; Uchida, K.; Saitoh, Eiji; Maekawa, Sadamichi

doi:10.1088/0034-4885/76/3/036501

Cited by 419 publications

(340 citation statements)

References 119 publications

(311 reference statements)

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“…Current theories on the origin of the spin Seebeck effect involve a nonequilibrium population of magnons accumulating at the interface between the magnetic insulator and metallic spin detector layer [31,36,37]. This could be due to several mechanisms, including bulk magnon diffusion [31] [38].…”

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Antiferromagnetic Spin Seebeck Effect

et al. 2016

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We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer it is possible to measure thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2 -80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T) are applied parallel the easy axis of the MnF2 thin film. When magnetic field is applied perpendicular to the easy axis, the spin flop transition is absent, as expected.

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Antiferromagnetic Spin Seebeck Effect

et al. 2016

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“…This behavior can be explained using the linear response theory of the SSE 16 as well as Boltzmann equation. 17,18 In this work the model reported by Adachi et al 16 is used to fit our experimental data, which considers the spin diffusion in the ferromagnet and obtains the thermal length scale of the magnon accumulation (K) from the magnon diffusion equation. Another parameter to take into account is the damping constant of the ferromagnet since it affects the distribution of magnon temperatures.…”

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“…15,16 According to this theory, two types of spin currents play the important role in the SSE: conduction electron spin current in the NM layer and magnon spin current in the FM layer. Adachi et al 16 described the magnon current in the FM using the Landau-Lifshitz-Gilbert equation, introducing the spinwave approximation, and projecting the magnon current onto the spin quantization axis. Using the proper boundary conditions they calculated the magnon and spin accumulation and therefore the magnonic current in the FM.…”

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

Anadón

Ramos

Lucas

et al. 2016

Applied Physics Letters

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The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K.

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“…To overcome the Joule heating [7] in current driven magnetization reversal, heat itself has recently been proposed [9] as an efficient control parameter for spin manipulation. A temperature gradient can generate spin current [10][11][12] due to electron and/or magnon flow. This thermoelectric phenomenon of spin current generation is called spin Seebeck effect that has been experimentally observed through the inverse spin Hall effect [10].…”

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Thermodynamic theory for thermal-gradient-driven domain-wall motion

Wang

2014

Phys. Rev. B

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Spin waves (or magnons) interact with magnetic domain walls (DWs) in a complicated way that a DW can propagate either along or against magnon flow. However, thermally activated magnons always drive a DW to the hotter region of a nanowire of magnetic insulators under a temperature gradient. We theoretically illustrate why it is surely so by showing that DW entropy is always larger than that of a domain as long as material parameters do not depend on spin textures. Equivalently, the total free energy of the wire can be lowered when the DW moves to the hotter region. The larger DW entropy is related to the increase of magnon density of states at low energy originated from the gapless magnon bound states. Manipulation of a magnetic domain wall (DW) in a nanostructure has attracted much attention due to its application prospects in logical operations [1] and data storage [2]. Moving DWs in a controlled manner is an important issue in those applications. Magnetic fields via energy dissipation [3][4][5] and electric current via angular momentum transfer [6][7][8] are well-known control parameters for DW motion. To overcome the Joule heating [7] in current driven magnetization reversal, heat itself has recently been proposed [9] as an efficient control parameter for spin manipulation. A temperature gradient can generate spin current [10][11][12] due to electron and/or magnon flow. This thermoelectric phenomenon of spin current generation is called spin Seebeck effect that has been experimentally observed through the inverse spin Hall effect [10]. The spin Seebeck effect has also been suggested [13,14] as a control parameter for DW manipulation. As spin-1 carriers, magnons can mediate a spin transfer torque (STT) [15] on a magnetic texture like a DW in a similar way as the electrons do. It was predicted [13,14] that a thermal-magnon-driven DW can propagate along a wire at a high speed, and this prediction was confirmed in a recent experiment [16].There is little doubt that magnonic STT can drive a DW to move. In terms of DW propagation direction, the pure magnonic STT predicts [15] a DW moving against magnon propagation direction. However, a DW may also propagate along magnon flow direction [17][18][19]. This is very similar to electric-current-driven DW motion: A DW propagates along or against electron flow direction, depending on detailed spin-orbit interactions and DW types [20][21][22]. It is not clear whether magnon-driven "wrong" DW propagation direction shares a similar physics origin as its electron counterpart. In principle, angular momentum does not dictate DW motion since its governing dynamics, Landau-Lifshitz-Gilbert (LLG) equation, does not conserve the total angular momentum when the spin-lattice and spin-orbital interactions are involved. Nevertheless, all studies [13,14,16] showed that a DW propagates to the hotter part of a wire under a temperature gradient. Although this result is consistent with the STT prediction, magnonic STT cannot be the sole physics behind. It is thus * Corresponding author: phxw...

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Theory of the spin Seebeck effect

Cited by 419 publications

References 119 publications

Antiferromagnetic Spin Seebeck Effect

Antiferromagnetic Spin Seebeck Effect

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

Thermodynamic theory for thermal-gradient-driven domain-wall motion

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