Control of current-induced spin-orbit effects in a ferromagnetic heterostructure by electric field

Liu, R. H.; Lim, W. L.; Urazhdin, Sergei

doi:10.1103/physrevb.89.220409

Cited by 68 publications

(57 citation statements)

References 39 publications

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“…It is also possible that the DMI at the Pt/[Co/Ni] interface neglected in our simulation stabilizes the DW spin structure of the skyrmion [15,23]. In addition, the current-induced field-like torque neglected in the simulation may provide a non-neglibible contribution stabilizing the skyrmion core [44]. Despite some quantitative discrepancies, our simulations confirm the possibility to create a stable dynamical skyrmion state in the SCAO [31].…”

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confidence: 63%

Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy

2015

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We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films. The possibility to induce dynamical states of nanomagnets or change their static configuration by the currentinduced spin torque (ST) [1, 2] has stimulated intense research into current-induced phenomena in magnetic systems. While the early experiments utilized spin-polarized electric currents in magnetic multilayers [3,4], recent studies focused on the effects of spin current produced due to the spin-orbit interaction (SOI) in bilayers of ferromagnets (F) with heavy nonmagnetic metals (N) [5][6][7][8]. The spin-orbit effects that contribute to the currentinduced phenomena include the spin Hall effect (SHE) originating from SOI in N, the Rashba effect [9] and the Dzyaloshinskii-Moriya interaction (DMI) [10], both originating from the broken inversion symmetry at the F/N interface. The DMI produces chiral effective fields that can result in nontrivial topological magnetic structures such as spirals, skyrmions and chiral domain walls [11].

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confidence: 63%

Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy

2015

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“…Substantial efforts have been expended in identifying the dominant mechanism for the spin-orbit torque. [30][31][32][33][34][35] For this purpose, one needs to go beyond qualitative analysis since both the mechanisms result in qualitatively identical predictions, i.e. two vector components of spin-orbit torque (see Eq.…”

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Angular dependence of spin-orbit spin-transfer torques

Lee

Manchon

et al. 2015

Phys. Rev. B

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In ferromagnet/heavy metal bilayers, an in-plane current gives rise to spin-orbit spin transfer torque which is usually decomposed into field-like and damping-like torques. For two-dimensional free-electron and tight-binding models with Rashba spin-orbit coupling, the field-like torque acquires nontrivial dependence on the magnetization direction when the Rashba spin-orbit coupling becomes comparable to the exchange interaction. This nontrivial angular dependence of the field-like torque is related to the Fermi surface distortion, determined by the ratio of the Rashba spin-orbit coupling to the exchange interaction. On the other hand, the damping-like torque acquires nontrivial angular dependence when the Rashba spin-orbit coupling is comparable to or stronger than the exchange interaction. It is related to the combined effects of the Fermi surface distortion and the Fermi sea contribution. The angular dependence is consistent with experimental observations and can be important to understand magnetization dynamics induced by spin-orbit spin transfer torques.

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“…There is of course the possibility of an additional source of spin-orbit torques that could arise from a spin-orbit interaction of the applied current at the NM/FM interface [11][12][13][14]. However, it has also been demonstrated that both spin-orbit torques decrease when a spacer layer is inserted between the heavy metal and the FM [10,15].…”

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Dependence of the efficiency of spin Hall torque on the transparency of Pt/ferromagnetic layer interfaces

et al. 2015

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We report that spin current transport across Pt-ferromagnet (FM) interfaces is strongly dependent on the type and the thickness of the FM layer and on post-deposition processing protocols. By employing both harmonic voltage measurements and spin-torque ferromagnetic resonance measurements, we find that the efficiency of the Pt spin Hall effect in exerting a damping-like spin torque on the FM ranges from < 0.05 to > 0.10 under different interfacial conditions. We also show that the temperature dependence of the spin torque efficiencies for both the dampinglike torque and field-like torque is dependent upon the details of the Pt-FM interface. The "internal" spin Hall angle of the Pt thin films used in this study, after taking the interfacial spin transmission factor into account, is estimated to be ~ 0.20. This suggests that a careful engineering of Pt-FM interfaces can improve the spin-Hall-torque efficiency of Pt-based spintronic devices. The spin Hall effect (SHE) [1, 2] causes an electrical current density e J flowing through a material with strong spin-orbit interactions to generate a transverse spin current density s J . The amplitude of s J is characterized by the spin Hall angle . The most straightforward way to determine a lower bound [3], θ SH LB , on the spin Hall angle in normal metal (NM) systems is to measure the current-dependent torque that is exerted on an adjacent ferromagnet (FM) when spin current flows to the NM-FM interface. Research has shown [4, 5]that there are two different components of torque that can be observed in this case: a "dampinglike" torque , where m is the orientation of the ferromagnetic moment, and a "field-like" torque . The determination via τ DL measurements of a large θ SH LB ≈ 0.07, in Pt-FM thin film bilayers [3, 6, 7], and the subsequent observation of even larger, "giant" spin Hall angles for high resistivity Ta (amorphous or β phase Ta), θ SH LB ≈ 0.12 [8] and β-W, θ SH LB ≈ 0.33 [9, 10], have opened up a very active area for research and technology development.Recent calculations utilizing Boltzmann analysis [11] and the drift-diffusion approximation [12] have noted that if the NM-FM interface is not completely transparent to the flow of the spin current then spin backflow will reduce the torque applied to the FM by the SHE.This reduction can be characterized, as suggested above, by defining a damping-like spin torque efficiency ξ DL , and also a field-like torque efficiency ξ FL , for a particular NM-FM interface, such that ξ DL can be less than or equal to the "internal" spin Hall angle θ SH that quantifies the spin current generated in the absence of an adjacent FM. Within a diffusive model, the effects of spin backflow are expected to modify the spin torque efficiencies in the form [11,12]

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Control of current-induced spin-orbit effects in a ferromagnetic heterostructure by electric field

Cited by 68 publications

References 39 publications

Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy

Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy

Angular dependence of spin-orbit spin-transfer torques

Dependence of the efficiency of spin Hall torque on the transparency of Pt/ferromagnetic layer interfaces

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