Spin hydrodynamics in amorphous magnets

Ochoa, Héctor; Zarzuela, Ricardo; Tserkovnyak, Yaroslav

doi:10.1103/physrevb.98.054424

Cited by 38 publications

(55 citation statements)

References 47 publications

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“…However, this so-called spin superfluid experiences energy loss via a spatially diffusing spin current, yet its uniform precessional frequency and linearly decaying spin current profile present potential advantages to the exponential decay property of magnons. Similar states have been predicted for antiferromagnets 7,8,21,22 and their experimental evidence in such materials has been recently presented 9,23 .…”

Section: Introductionsupporting

confidence: 79%

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Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: Role of dispersion, nonlinearity, and damping

Iacocca

Hoefer

2019

Phys. Rev. B

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Nonlocal compensation of magnetic damping by spin injection has been theoretically shown to establish dynamic, noncollinear magnetization states that carry spin currents over micrometer distances. Such states can be generically referred to as dissipative exchange flows (DEFs) because spatially diffusing spin currents are established by the mutual exchange torque exerted by neighboring spins. Analytical studies to date have been limited to the weak spin injection assumption whereby the equation of motion for the magnetization is mapped to hydrodynamic equations describing spin flow and then linearized. Here, we analytically and numerically study easy-plane ferromagnetic channels subject to spin injection of arbitrary strength at one extremum under a unified hydrodynamic framework. We find that DEFs generally exhibit a nonlinear profile along the channel accompanied by a nonlinear frequency tuneability. At large injection strengths, we fully characterize a novel magnetization state we call a contact-soliton DEF (CS-DEF) composed of a stationary soliton at the injection site, which smoothly transitions into a DEF and exhibits a negative frequency tuneability. The transition between a DEF and a CS-DEF occurs at the maximum precessional frequency and coincides with the Landau criterion: a subsonic to supersonic flow transition. Leveraging the hydraulic-electrical analogy, the current-voltage characteristics of a nonlinear DEF circuit are presented. Micromagnetic simulations of nanowires that include magnetocrystalline anisotropy and non-local dipole fields are in qualitative agreement with the analytical results. The magnetization states found here along with their characteristic profile and spectral features provide quantitative guidelines to pursue an experimental demonstration of DEFs in ferromagnetic materials and establishes a unified description for long-distance spin transport.

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Section: Introductionsupporting

confidence: 79%

“…that can be solved numerically as a function ofū given the boundary and matching conditions (21a), (21b), and (22). Figure 4 depicts the boundary layer width as a function ofū larger thanū max , where the CS-DEF solution occurs in a channel of length L = 100.…”

Section: Fig 4 (Color Online) Boundary Layer Width As a Function Ofmentioning

confidence: 99%

Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: Role of dispersion, nonlinearity, and damping

Iacocca

Hoefer

2019

Phys. Rev. B

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“…For the final result, we have used the ansatz given in the main text. We model dissipation by means of the Gilbert-Rayleigh function [7]…”

Section: Collective-variable Approach For Skyrmionsmentioning

confidence: 99%

“…Discussion.-The channel for spin transport rooted in the diffusion of skyrmion charge becomes suppressed in the low-temperature regime, as the proliferation of skyrmions in the bulk of the magnet dies out with probability ∝ e −E sky /kBT . The frustrated magnet, however, sustains stable spin supercurrents at low temperatures in the presence of additional easy-plane anisotropies; this coherent transport of spin may be driven by nonequilibrium spin accumulations at the left interface, which are induced by the charge current flowing within the first terminal via the spin Hall effect [7]. Furthermore, in the absence of topological singularities in the SO(3) order parameter (namely, Z 2 vortices) degradation of the spin superflow only occurs via thermally-activated phase slips in the form of 4π-vortex lines [7].…”

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confidence: 99%

Hydrodynamics of three-dimensional skyrmions in frustrated magnets

2019

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We study the nucleation and collective dynamics of Shankar skyrmions [R. Shankar, Journal de Physique 38, 1405(1977] in the class of frustrated magnetic systems described by an SO(3) order parameter, including multi-lattice antiferromagnets and amorphous magnets. We infer the expression for the spin-transfer torque that injects skyrmion charge into the system and the Onsagerreciprocal pumping force that enables its detection by electrical means. The thermally-assisted flow of topological charge gives rise to an algebraically decaying drag signal in nonlocal transport measurements. We contrast our findings to analogous effects mediated by spin supercurrents. arXiv:1901.01208v1 [cond-mat.mes-hall]

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“…The field of spin hydrodynamics is undergoing rapid theoretical development that has lead to realistic predictions in various contexts. While this review has emphasized ferromagnetic materials, spin hydrodynamics have been extended beyond, including spin transport in antiferromagnets [83,84], noncollinear antiferromagnets [85], and amorphous materials [86]. These early works have already demonstrated that the hydrodynamic perspective of nonlinear dynamics in magnetic materials results from a distinctly new interpretation that yields significant predictive value.…”

Section: Perspectives and Challengesmentioning

confidence: 99%

Perspectives on spin hydrodynamics in ferromagnetic materials

Iacocca

Hoefer

2019

Physics Letters A

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The field of spin hydrodynamics aims to describe magnetization dynamics from a fluid perspective. For ferromagnetic materials, there is an exact mapping between the Landau-Lifshitz equation and a set of dispersive hydrodynamic equations. This analogy provides ample opportunities to explore novel magnetization dynamics and magnetization states that can lead to applications relying entirely upon magnetic materials, for example, long-distance transport of information. This article provides an overview of the theoretical foundations of spin hydrodynamics and their physical interpretation in the context of spin transport. We discuss other proposed applications for spin hydrodynamics as well as our view on challenges and future research directions. arXiv:1909.05756v1 [cond-mat.mes-hall] 12 Sep 2019 and the spin pumping [11,12] effects provide an interconversion mechanism between angular momentum and charge currents at a magnet / metal interface. A technological advantage of spin waves is that their existence is independent of the conduction properties of the material. This implies that energy dissipation associated to conduction electrons is minimized. However, spin waves are subject to scattering processes that ultimately limit their coherence [13].The amplitude of a spin wave decays exponentially with a decay length equal to v g /(2ωα) [14], where v g , ω, and α are, respectively, the spin wave group velocity, angular frequency, and the magnetic Gilbert damping parameter [15]. To maximize the decay length, low damping materials such as Permalloy (Ni 80 Fe 20 ) and YIG have been regularly used for research on all-magnetic logic and computation [16]. Decay lengths on the order of micrometers have been obtained in these materials [14,17,18]. Recently, long-distance spin transport in amorphous Yttrium-Iron ferrite [19] and antiferromagnetic haematite [20] was measured experimentally. However, the finite Gilbert damping parameter and the concomitant exponential decay of spin waves remains a presently insurmountable limitation for magnon-based technologies.To beat exponential decay, other forms of spin transport must be explored. Spin hydrodynamics offers such an alternative via the stabilization of noncollinear, large-amplitude magnetization states in magnetic materials with dominant easy-plane anisotropy. Because of its potential impact on technologies that rely on the control of spin, the field of spin hydrodynamics has experienced a rapid growth over the last five years, including recent experimental evidence [21,22] for hydrodynamic-like spin transport.In light of multiple recent theoretical developments, we provide in this article an overview of the theoretical studies on spin hydrodynamics in ferromagnetic materials. We review the dispersive hydrodynamic formulation of magnetization dynamics and its physical interpretation. We also discuss the theoretical predictions pertaining to the properties of ideal and current-induced spin hydrodynamic states in the context of long-distance spin transport. Finally, we discuss ...

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Spin hydrodynamics in amorphous magnets

Cited by 38 publications

References 47 publications

Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: Role of dispersion, nonlinearity, and damping

Hydrodynamic description of long-distance spin transport through noncollinear magnetization states: Role of dispersion, nonlinearity, and damping

Hydrodynamics of three-dimensional skyrmions in frustrated magnets

Perspectives on spin hydrodynamics in ferromagnetic materials

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