Field dependence of magnetization reversal by spin transfer

Grollier, Julie; Cros, Vincent; Jaffrès, H.; Hamzić, Amir; George, Jean-Marie; Faini, G.; Youssef, J. Ben; Gall, H. Le; Fert, A.

doi:10.1103/physrevb.67.174402

Cited by 198 publications

(154 citation statements)

References 34 publications

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“…The potential application of the latter structure as a nonvolatile magnetic memory motivates the development of detailed models for the theoretical mechanisms underlying CIMS. Most of the present models [9,10,11,12,13] agree on the fact that the Landau-Lifshitz-Gilbert (LLG) equation can be modified by a current-dependent term. This term acts either as a torque, an effective field or leads to spin transfer by a relaxation process.…”

mentioning

confidence: 90%

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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confidence: 90%

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

et al. 2003

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“…23 In order to understand what type of motions may be associated with the different dynamical modes, we have computed solutions of the Landau-Lifshitz-Gilbert equation of 6 motion for a single-domain magnet. [24][25][26][27] We employ the form of the spin-transfer torque derived in [1]. The calculated zero-temperature dynamical phase diagram is presented in Fig.…”

Section: † These Authors Contributed Equally To This Workmentioning

confidence: 99%

Microwave oscillations of a nanomagnet driven by a spin-polarized current

Kiselev

Sankey

Krivorotov

et al. 2003

Nature

1,976

1,595

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† These authors contributed equally to this workThe recent discovery that a spin-polarized electrical current can apply a large torque to a ferromagnet, through direct transfer of spin angular momentum, offers the intriguing possibility of manipulating magnetic-device elements without applying cumbersome magnetic fields. 1-16 However, a central question remains unresolved:What type of magnetic motions can be generated by this torque? Theory predicts that spin transfer may be able to drive a nanomagnet into types of oscillatory magnetic modes not attainable with magnetic fields alone, 1-3 but existing measurement techniques have provided only indirect evidence for dynamical states. 4,6-8,12,14-16 The nature of the possible motions has not been determined. Here we demonstrate a technique that allows direct electrical measurements of microwave-frequency dynamics in individual nanomagnets, propelled by a DC spin-polarised current. We show that in fact spin transfer can produce several different types of magnetic excitations. Although there is no mechanical motion, a simple magnetic-multilayer structure acts like a nanoscale motor; it converts energy from a DC electrical current into high-frequency magnetic rotations that might be applied in new devices including microwave sources and resonators. 2 We examine samples made by sputtering a multilayer of 80 nm Cu / 40 nm Co / 10 nm Cu / 3 nm Co / 2 nm Cu / 30 nm Pt onto an oxidized silicon wafer and then milling through part of the multilayer (Fig. 1a) to form a pillar with an elliptical cross section of lithographic dimensions 130 nm ¥ 70 nm. 17 Top contact is made with a Cu electrode.Transmission or reflection of electrons from the thicker "fixed" Co layer produces a spinpolarised current that can apply a torque to the thinner "free" Co layer. Subsequent oscillations of the free-layer magnetization relative to the fixed layer change the device resistance 18 so, under conditions of DC current bias, magnetic dynamics produce a timevarying voltage (with typical frequencies in the microwave range). If the oscillations were exactly symmetric relative to the direction to the fixed-layer moment, voltage signals would occur only at multiples of twice the fundamental oscillation frequency, f. To produce signal strength at f, we apply static magnetic fields (H) in the sample plane a few degrees away from the magnetically-easy axis of the free layer. All data are taken at room temperature, and by convention positive current I denotes electron flow from the free to the fixed layer.In characterization measurements done at frequencies < 1 kHz, the samples exhibit the same spin-transfer-driven changes in resistance reported in previous experiments 7,9 (Fig. 1b). For H smaller than the coercive field of the free layer (H c ~ 600 Oe), an applied current produces hysteretic switching of the magnetic layers between the low-resistance parallel (P) and high-resistance antiparallel (AP) states. Sweeping H can also drive switching between the P and AP states (Fig 1b, inset). For H larger ...

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“…Other observed dynamical behavior includes telegraph noise that is interpreted as rapid switching between two distinct states of magnetization. 16,17,18,19 Several experimental groups have used the macrospin (single domain) approximation to propose "phase diagrams" that identify the dynamical state of their spin valves as a function of J and H. 8,11,17,19,20,21,22,23 There have also been purely theoretical studies of the LLG equation (generalized to include spin-transfer torque) using both macrospin models 24,25,26,27,28,29,30 and micromagnetics simulations 31,32,33,34,35,36,37,38 that do not make the single-domain approximation. Unfortunately, it is difficult to extract a coherent picture from all this work because different authors make different choices for the physical effects they believe most affect the dynamics.…”

Section: Introductionmentioning

confidence: 99%

Macrospin models of spin transfer dynamics

2005

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The current-induced magnetization dynamics of a spin valve are studied using a macrospin (single domain) approximation and numerical solutions of a generalized Landau-Lifshitz-Gilbert equation. (2003)], we calculate the resistance and microwave power as a function of current and external field including the effects of anisotropies, damping, spin-transfer torque, thermal fluctuations, spin-pumping, and incomplete absorption of transverse spin current. While many features of experiment appear in the simulations, there are two significant discrepancies: the current dependence of the precession frequency and the presence/absence of a microwave quiet magnetic phase with a distinct magnetoresistance signature. Comparison is made with micromagnetic simulations designed to model the same experiment.

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Field dependence of magnetization reversal by spin transfer

Cited by 198 publications

References 34 publications

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

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

Microwave oscillations of a nanomagnet driven by a spin-polarized current

Macrospin models of spin transfer dynamics

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