Thermal generation of spin current in epitaxial CoFe2O4 thin films

Guo, Er‐Jia; Herklotz, Andreas; Kehlberger, Andreas; Cramer, Joel; Jakob, G.; Kläui, Mathias

doi:10.1063/1.4939625

Cited by 31 publications

(21 citation statements)

References 35 publications

(62 reference statements)

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“…The normalized spin Seebeck coefficient saturates as a function of d on the scale of the magnon spin diffusion length m . While experiments at T 0 250 K report somewhat smaller length scales than our m , our saturation σ SSE ∼ 0.1-1 μV/K is of the same order as the experiments [51].…”

Section: Longitudinal Spin Seebeck Effectsupporting

confidence: 66%

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

et al. 2016

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We develop a linear-response transport theory of diffusive spin and heat transport by magnons in magnetic insulators with metallic contacts. The magnons are described by a position dependent temperature and chemical potential that are governed by diffusion equations with characteristic relaxation lengths. Proceeding from a linearized Boltzmann equation, we derive expressions for length scales and transport coefficients. For yttrium iron garnet (YIG) at room temperature we find that long-range transport is dominated by the magnon chemical potential. We compare the model's results with recent experiments on YIG with Pt contacts [L. J. Cornelissen, et al., Nat. Phys. 11, 1022] and extract a magnon spin conductivity of σm = 5 × 10 5 S/m. Our results for the spin Seebeck coefficient in YIG agree with published experiments. We conclude that the magnon chemical potential is an essential ingredient for energy and spin transport in magnetic insulators.

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Section: Longitudinal Spin Seebeck Effectsupporting

confidence: 66%

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

et al. 2016

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“…It is widely used in high-frequency systems and as inductors in conventional applications. 17 Recently, NFO and other spinel ferrites were explored for spintronics applications, where effects like spin Hall magnetoresistance (SMR), [18][19][20][21][22] SSE [23][24][25][26][27][28][29][30] and nonlocal magnon spin transport 15 were reported. In most of these studies, large magnetic fields of a few teslas are required to align the magnetization of the ferrites, possibly due to the presence of antiphase boundaries.…”

mentioning

confidence: 99%

Enhanced magnon spin transport in NiFe2O4 thin films on a lattice-matched substrate

Shan

Singh

Lei

et al. 2018

Applied Physics Letters

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We investigate magnon spin transport in epitaxial nickel ferrite (NiFe 2 O 4 , NFO) films grown on magnesium gallate spinel (MgGa 2 O 4 , MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%, resulting in the reduction of antiphase boundary defects and thus in improved magnetic properties in the NFO films. In the nonlocal transport experiments, enhanced signals are observed for both electrically and thermally excited magnons, and the magnon relaxation length (λ m ) of NFO is found to be around 2.5 µm at room temperature. Moreover, at both room and low temperatures, we present distinct features from the nonlocal spin Seebeck signals which arise from magnonpolaron formation. Our results demonstrate excellent magnon transport properties (magnon spin conductivity, λ m and spin mixing conductance at the interface between Pt) of NFO films grown on a lattice-matched substrate that are comparable with those of yttrium iron garnet.

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“…Previously, SSE has been observed in ferrites and a) j.shan@rug.nl other magnetic spinels. [26][27][28][29][30][31][32] However, the nonlocal transport of magnon spin has not yet been explored in ferrite systems.In this study, we focus on the NFO thin film systems which can be prepared by co-sputtering, 33 whereby a typical bandgap of 1.49 eV and a resistivity of 40 Ω·m can be obtained at room temperature. 34 The electrical properties of the NFO films can be further tuned by temperature 26 or oxygen contents.…”

mentioning

confidence: 99%

“…It is known that in an inverse spinel magnetic thin film with (001) orientation, a four-fold magnetic anisotropy is expected in-plane, with two magnetic easy axes aligned perpendicular to each other. 26,27 Figure 1(a) plots the NFO magnetization when an in-plane magnetic field is applied along one of the magnetic hard axes, showing a coercive field of around 0.2 T.To study the magnon spin transport in the NFO, two Pt strips, parallel to each other and separated by a center-tocenter distance d, were patterned by e-beam lithography and grown on the NFO layer by dc sputtering. The Pt strips are all oriented along one of the magnetic hard axes.…”

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confidence: 99%

Nonlocal magnon spin transport in NiFe2O4 thin films

Shan

Bougiatioti

Lei

et al. 2017

Applied Physics Letters

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We report magnon spin transport in nickel ferrite (NiFe 2 O 4 , NFO)/ platinum (Pt) bilayer systems at room temperature. A nonlocal geometry is employed, where the magnons are excited by the spin Hall effect or by the Joule heating induced spin Seebeck effect at the Pt injector, and detected at a certain distance away by the inverse spin Hall effect at the Pt detector. The dependence of the nonlocal magnon spin signals as a function of the magnetic field is closely related to the NFO magnetization behavior. In contrast, we observe that the magnetoresistance measured locally at the Pt injector does not show a clear relation with the average NFO magnetization. We obtain a magnon spin relaxation length of 3.1 ± 0.2 µm in the investigated NFO samples.The transport of spin information is one of the most extensively studied topics in the field of spintronics.1,2 Spin current, a flow of angular momentum, is a non-conserved quantity that is mostly transported diffusively in various material systems, regardless of the carrier being conduction electrons or quasiparticles such as magnons. 3 In traditional metallic systems 4 and 2D materials such as graphene, 5 a nonlocal spin valve geometry is usually applied to study the spin diffusion phenomena and their relevant length scales.Very recently, it was shown that thermal magnons with typical frequencies of around k B T /h can be excited and detected purely electrically in Pt/yttrium iron garnet (YIG) systems, by also employing a nonlocal geometry where the injector and detector are both Pt strips, spaced at a certain distance.3,6-9 An electric current through the injector excites non-equilibrium magnons both electrically via the spin Hall effect (SHE) 10,11 and thermally via the spin Seebeck effect (SSE), 12-14 and they are detected nonlocally via the inverse spin Hall effect (ISHE). 15 At room temperature and below, 16 a magnon relaxation length λ m of typically around 10 µm is observed, for both electrically and thermally generated magnons independent from the YIG thickness. 17 An open question is whether the nonlocal effects can be also observed in other magnetic materials, such as ferrites, being ferrimagnetic at room temperature with a relatively large bandgap. Two local effects have been studied in Pt/ferrite systems so far: the first is the spin Hall magnetoresistance (SMR), 18-21 which results from the simultaneous action of SHE and ISHE in the Pt layer, while the magnetization in the magnetic substrate modifies the spin accumulation at the interface and hence the Pt resistance. SMR has been reported in Pt/NiFe 2 O 4 (NFO), Pt/Fe 3 O 4 and Pt/CoFe 2 O 4 systems. 20,[22][23][24] Second is the SSE, one of the central topics in the field of spin caloritronics, 25 which is the excitation of magnon currents when exerting a temperature gradient on the magnetic material. Previously, SSE has been observed in ferrites and a) j.shan@rug.nl other magnetic spinels.26-32 However, the nonlocal transport of magnon spin has not yet been explored in ferrite systems.In this study, we ...

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Thermal generation of spin current in epitaxial CoFe2O4 thin films

Cited by 31 publications

References 35 publications

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

Magnon spin transport driven by the magnon chemical potential in a magnetic insulator

Enhanced magnon spin transport in NiFe2O4 thin films on a lattice-matched substrate

Nonlocal magnon spin transport in NiFe2O4 thin films

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