Exchange torque and spin transfer between spin polarized current and ferromagnetic layers

Wegrowe, Jean-Eric; Fabian, A. C.; Guittienne, Ph.; Hoffer, X.; Kelly, Derek M.; Ansermet, Jean-Philippe; Olive, Enrick

doi:10.1063/1.1476065

Cited by 53 publications

(42 citation statements)

References 15 publications

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“…The metastable characteristics of the magnetization of the thin Co layer can be described by the Néel-Brown activation process [21]. The energy barrier depends on the shape and magnetocrystalline anisotropy, on the external field and on the dipole field due to the pinned layer [18]. At low current, the spin-valve is stable and does not show TLF.…”

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confidence: 99%

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Current-Induced Two-Level Fluctuations in Pseudo-Spin-Valve (Co/Cu/Co) Nanostructures

et al. 2003

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Two-level fluctuations of the magnetization state of pseudo spin-valve pillars Co(10 nm)/Cu(10 nm)/Co(30 nm) embedded in electrodeposited nanowires (∼ 40 nm in diameter, 6000 nm in length) are triggered by spin-polarized currents of 10 7 A/cm 2 at room temperature. The statistical properties of the residence times in the parallel and antiparallel magnetization states reveal two effects with qualitatively different dependences on current intensity. The current appears to have the effect of a field determined as the bias field required to equalize these times. The bias field changes sign when the current polarity is reversed. At this field, the effect of a current density of 10 7 A/cm 2 is to lower the mean time for switching down to the microsecond range. This effect is independent of the sign of the current and is interpreted in terms of an effective temperature for the magnetization.

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“…A uniaxial magnetocrystalline anisotropy can be obtained [18]. Thus, the spin-valve behaves as a two-state system defined by the two relative orientations of the magnetic layers.…”

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Current-Induced Two-Level Fluctuations in Pseudo-Spin-Valve (Co/Cu/Co) Nanostructures

et al. 2003

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“…The source of the spin polarized current can either be a different ferromagnet, or, for a thick magnet, a region of the same ferromagnet upstream or downstream in the current flow. The "spin-transfer torque" gives rise to magnetization reversal in ferromagnet-normal-metal-ferromagnet trilayers [1, 2], which has been observed experimentally by several groups [4,5,6,7,8,9,10]. Dynamic manifestations of the spin-transfer torque include domain wall motion in bulk ferromagnets [11,12,13,14] and the excitation of spin waves by polarized currents in ferromagnetic multilayers or wires [2,3,4,5,6,7,8,15,16,17].…”

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Current-Induced Transverse Spin-Wave Instability in a Thin Nanomagnet

2004

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We show that an unpolarized electric current incident perpendicular to the plane of a thin ferromagnet can excite a spin-wave instability transverse to the current direction if source and drain contacts are not symmetric. The instability, which is driven by the current-induced "spin-transfer torque", exists for one current direction only.PACS numbers: 75.75.+a, 75.40.Gb, Ferromagnets serve as spin filters for an electrical current passing through the magnet: the spin of the electrons that are transmitted through a ferromagnet becomes partially polarized parallel or antiparallel to the direction of the magnetization whereas spin current perpendicular to the magnetization direction is absorbed. Spin filtering is the root cause for the "spintransfer torque", the phenomenon that a polarized current impinging on a ferromagnet affects its magnetization direction [1,2,3]. The source of the spin polarized current can either be a different ferromagnet, or, for a thick magnet, a region of the same ferromagnet upstream or downstream in the current flow. The "spin-transfer torque" gives rise to magnetization reversal in ferromagnet-normal-metal-ferromagnet trilayers [1, 2], which has been observed experimentally by several groups [4,5,6,7,8,9,10]. Dynamic manifestations of the spin-transfer torque include domain wall motion in bulk ferromagnets [11,12,13,14] and the excitation of spin waves by polarized currents in ferromagnetic multilayers or wires [2,3,4,5,6,7,8,15,16,17]. In all these manifestations, the current-induced spin torque can be distinguished from effects arising from the current induced magnetic field, the main difference being that spintransfer torque effects depend on the current direction, whereas magnetic field induced effects do not.In this letter, we show that an unpolarized current can also exert a spin-transfer torque on a ferromagnet, even if the magnet is so thin that its magnetization direction does not change along the current flow: Although an unpolarized current cannot exert a spin-transfer torque that changes the over-all magnetization direction, it can create a transverse spin wave instability for sufficiently high current densities if the source and drain contacts to the ferromagnet are not symmetric. This spin wave instability can be identified unambiguously as a spin-torque effect because of its dependence on current direction: the spin-wave instability is present for one current direction and absent for the other. The spin-wave instability should lead to a non-hysteretic feature in the currentvoltage characteristic of the ferromagnetic film that exists for one current direction only. In thick ferromagnets, such features have been observed in recent experiments [4,17] instability, asymmetric contacts to source and drain, is generically fulfilled in experiments on nanoscale magnets [5]. The issue of current-induced spin-wave excitation has significant practical relevance for devices based on the spin-torque effect in ferromagnetic multilayers. Whereas, experimentally, the presence of dynamica...

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“…However, because of its inherent simplicity, and the small lateral sizes of the pores (as little as 10 nm), it offered the first controllable route to CPP measurements of GMR devices. More recently, the process has been developed to enable the measurement of STT in individual nanowires [12,13]. High-density ordered arrays can also be achieved using alumina templates [14].…”

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confidence: 99%