Asymmetric Pt/Co/Pt-stack induced sign-control of current-induced magnetic domain-wall creep

Lavrijsen, Reinoud; Haazen, Ppj; Murè, E.; Franken, JH Jeroen; Swagten, Hjm Henk; Koopmans, B.

doi:10.1063/1.4732083

Cited by 35 publications

(35 citation statements)

References 27 publications

(39 reference statements)

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“…Current-assisted DW motion opposing electron flow has also been reported in asymmetric Pt/Co/Pt trilayers with thicker Pt at the bottom layer [28,29,34] and in Pt/Co(ferromagnet)/oxide(insulator) trilayers with Pt at the bottom [19-22, 39, 43-45]. A nonuniform current distribution due to the asymmetric layer structure may produce an internal electric potential, which then may generate an effective Rashba field in the ultrathin ferromagnet [67,68].…”

Section: Origin Of Current-induced Torques In Co/ptmentioning

confidence: 99%

“…Furthermore, the spin-torque efficiencies for Co/Pt multilayers with different Co layer thicknesses resolve the disparity in recent studies of currentinduced DW dynamics in Co/Pt, some reporting high spin-torque efficiencies of over 10 Oe/10 11 A/m 2 [23,24,26,29,34] while others showing no effects other than Joule heating [19, 30-34, 38, 39]. Our results suggest that the inplane current through the ultrathin ferromagnetic layers attains a vanishingly small effective spin polarization, consistent with the rigorous semi-classical calculations by Cormier et al [32] and the recent experimental findings by Tanigawa et al [16] In ultrathin Co/Pt-based structures, conventional spintransfer torques (STTs) are likely not present, and the current-induced torque from the spin Hall effect [56,57] drives DWs as reported in recent studies [42-45, 53, 58].…”

Section: Introductionmentioning

confidence: 99%

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Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers

Emori

Umachi

Bono

et al. 2015

Journal of Magnetism and Magnetic Materials

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Thermally activated domain-wall (DW) motion driven by magnetic field and electric current is investigated experimentally in out-of-plane magnetized Pt(Co/Pt) 3 multilayers. We directly extract the thermal activation energy barrier for DW motion and observe the dynamic regimes of creep, depinning, and viscous flow. Further analysis reveals that the activation energy must be corrected with a factor dependent on the Curie temperature, and we derive a generalized Arrhenius-like equation governing thermally activated motion. By using this generalized equation, we quantify the efficiency of currentinduced spin torque in assisting DW motion. Current produces no effect aside from Joule heating in the multilayer with 7-Å thick Co layers, whereas it generates a finite spin torque on DWs in the multilayer with atomically thin 3-Å Co layers. These findings suggest that conventional spin-transfer torques from in-plane spin-polarized current do not drive DWs in ultrathin Co/Pt multilayers.

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Section: Origin Of Current-induced Torques In Co/ptmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers

Emori

Umachi

Bono

et al. 2015

Journal of Magnetism and Magnetic Materials

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“…29 Attempts to develop predictive models face the complication that the experimental structures deviate significantly from the ideal structures treated theoretically. Experimental indications 30,31 that interfaces of Co grown on Pt have different properties than interfaces of Pt grown on Co argue strongly that the details of the interface structure are both nontrivial and important. Unfortunately, the interfaces are not well enough characterized to know what types of disorder might be present.…”

Section: Introductionmentioning

confidence: 99%

Current induced torques and interfacial spin-orbit coupling: Semiclassical modeling

et al. 2013

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In bilayer nanowires consisting of a ferromagnetic layer and a nonmagnetic layer with strong spin-orbit coupling, currents create torques on the magnetization beyond those found in simple ferromagnetic nanowires. The resulting magnetic dynamics appear to require torques that can be separated into two terms, dampinglike and fieldlike. The dampinglike torque is typically derived from models describing the bulk spin Hall effect and the spin transfer torque, and the fieldlike torque is typically derived from a Rashba model describing interfacial spin-orbit coupling. We derive a model based on the Boltzmann equation that unifies these approaches. We also consider an approximation to the Boltzmann equation, the drift-diffusion model, that qualitatively reproduces the behavior, but quantitatively differs in some regimes. We show that the Boltzmann equation with physically reasonable parameters can match the torques for any particular sample, but in some cases, it fails to describe the experimentally observed thickness dependencies.

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“…This may be attributed to its thinner bottom Pt layer which results in a rougher surface morphology and slightly degraded Pt/Co interface quality as compared to sample B. 24 Consequently, sample A will have a weaker than expected spin current generation from the bottom Pt layer and less spin current cancellation with the top Pt layer. Assuming that ∆H L originates solely from SHE, the net spin current will be approximately 40% of the bulk based on the drift-diffusion theory 21 and using a spin diffusion length of Pt = 1.4nm.…”

mentioning

confidence: 99%

Asymmetry in effective fields of spin-orbit torques in Pt/Co/Pt stacks

Sim¹,

Huang²,

Tran³

et al. 2014

Appl. Phys. Lett.

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Measurements of switching via spin-orbit coupling (SOC) mechanisms are discussed for a pair of inverted Pt/Co/Pt stacks with asymmetrical Pt thicknesses. Taking into account the planar Hall effect contribution, effective fields of spin-orbit torques (SOT) are evaluated using lock-in measurements of the first and second harmonics of the Hall voltage. Reversing the stack structure leads to significant asymmetries in the switching behavior, including clear evidence of a nonlinear current dependence of the transverse effective field. Our results demonstrate potentially complex interplay in devices with all-metallic interfaces utilizing SOT.Current-induced spin-orbit torques (SOTs) provide a novel alternative route to conventional spin-transfer torque to manipulate magnetization of a single ferromagnetic layer. Experiments have demonstrated unambiguously that in a system consisting of a bilayer interface with both a ferromagnet and a high strong spin-orbit coupling (SOC) material, stable magnetization reversal, 1,2 high frequency spin wave oscillations, 3 as well as ultrafast domain wall motion 4-6 can be achieved without an additional non-collinear reference ferromagnet. There are at least two mechanisms generally believed to lead to the observed SOTs, including the spin-Hall and Rashba effects. In the case of the spin-Hall effect (SHE), spin dependent scattering of a lateral electrical current generates spin currents directed towards the boundaries. The component of spin current normal to the heavy-metal (HM)/ferromagnet (FM) interface, consequently is injected into the ferromagnetic layer. 8 However, in the Rashba picture, a lateral electrical current flow creates a nonlocal out-of-equilibrium spin density at the HM/FM interface due to a strong electric field gradient in film stacks having structural inversion asymmetry (SIA), 7 illustrated in Fig. 1. In both cases, the s − d exchange interaction between these injected polarized (and/or nonequilibrium) spins and localized 3d electrons in the adjacent ferromagnet generates a SOT, equivalent to effective fields in the film plane, which acts on the magnetization.Because SHE injects a spin-current into the ferromagnet, itinerant transversely polarized spins (⊥ to both M and spin polarization p) scatter and accumulate at the HM/FM interface. Therefore, the dominant effective field behaves as p × m, i.e. ∆H L ∝ p × m. In the Rashba picture, without spin injection, the dominant torque is expected to follow p symmetry (i.e. ∆H T ∝ p). Thus, torque due to the transverse effective field ∆H T , which is orthogonal to the current flow J, has symmetry similar to the classical field-like torque in magnetic tunnel junctions, 9 while the spin-Hall effect, generating a longitudinal effective field ∆H L parallel to current flow, leads to a torque with the same symmetry as the Slona) Electronic address: SIM Cheow Hin@dsi.a-star.edu.sg czewski torque. 1 In a recent systematic thickness dependence study in a Ta/CoFeB/MgO stack, Kim et al . observed a transverse effective field closely...

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Asymmetric Pt/Co/Pt-stack induced sign-control of current-induced magnetic domain-wall creep

Cited by 35 publications

References 27 publications

Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers

Generalized analysis of thermally activated domain-wall motion in Co/Pt multilayers

Current induced torques and interfacial spin-orbit coupling: Semiclassical modeling

Asymmetry in effective fields of spin-orbit torques in Pt/Co/Pt stacks

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