Spin-current interaction with a monodomain magnetic body: A model study

Sun, J. Z.

doi:10.1103/physrevb.62.570

Cited by 1,011 publications

(771 citation statements)

References 9 publications

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“…This can excite and even switch the magnetization direction of the softer ferromagnet. Experiments with pillar-type structures [6][7][8] confirmed these predictions.…”

Section: Introductionsupporting

confidence: 72%

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

et al. 2008

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We describe electrical detection of spin pumping in metallic nanostructures. In the spin pumping effect, a precessing ferromagnet attached to a normal metal acts as a pump of spin-polarized current, giving rise to a spin accumulation. The resulting spin accumulation induces a backflow of spin current into the ferromagnet and generates a dc voltage due to the spin dependent conductivities of the ferromagnet. The magnitude of such voltage is proportional to the spin-relaxation properties of the normal metal. By using platinum as a contact material we observe, in agreement with theory, that the voltage is significantly reduced as compared to the case when aluminum was used. Furthermore, the effects of rectification between the circulating rf currents and the magnetization precession of the ferromagnet are examined. Most significantly, we show that using an improved layout device geometry, these effects can be minimized.

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“…This can excite and even switch the magnetization direction of the softer ferromagnet. Experiments with pillar-type structures [6][7][8] confirmed these predictions.…”

Section: Introductionsupporting

confidence: 72%

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

et al. 2008

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“…torque-induced magnetization dynamics, is called linear analysis of the LLG equation 9,17,21 . In this approach, the spin torque is assumed to cancel the damping torque when the current magnitude equals that of the threshold current.…”

Section: Pacs Numbersmentioning

confidence: 99%

Crossover between fast and slow excitation of magnetization by spin torque

Taniguchi¹

2016

Appl. Phys. Express

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A crossover between two mechanisms destabilizing the magnetization in equilibrium by the spin transfer effect is found in a ferromagnetic multilayer consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer, where an in-plane magnetic field is applied, and electric current flows from the pinned to the free layer. A fast transition from the in-plane to the out-of-plane state occurs in the low-field region, whereas a slow transition with small-amplitude oscillation becomes dominant in the high-field region. On the other hand, only the fast transition mechanism appears for the opposite current direction. PACS numbers:Excitation of magnetization dynamics such as switching and self-oscillation in a ferromagnetic/nonmagnetic multilayer by the spin transfer effect 1,2 has been studied extensively for application in practical devices such as magnetic memory and microwave generators 3-15 . It has been recognized that there is a threshold value of the electric current necessary to destabilize the magnetization in equilibrium and excite any type of magnetization dynamics by the spin torque effect. Evaluation of the threshold current is important because it determines the performance of spin torque devices, for example, power consumption. To this end, a deep understanding of the physical mechanism of magnetization instability due to the spin torque is necessary.In this letter, the physical mechanism destabilizing the magnetization in a ferromagnetic multilayer consisting of an in-plane magnetized free layer and a perpendicularly magnetized pinned layer is studied theoretically. We find that this system shows a crossover between two mechanisms destabilizing the magnetization in equilibrium, depending on the magnitude of an in-plane applied magnetic field. A fast transition, on the order of nanoseconds, from an in-plane stable state to an out-ofplane state is dominant in the low-field region, whereas a slow transition in a time range exceeding 100 ns with a small-amplitude oscillation principally determines the instability threshold in the high-field region. This crossover appears only when the electric current flows perpendicular to the plane from the pinned layer to the free layer. When the current direction is reversed, the instability threshold is determined solely by the fast transition. Figure 1 schematically shows the system under consideration. The z-axis is perpendicular to the film-plane, and an in-plane magnetic field is applied along the x-axis. The unit vectors pointing in the magnetization directions of the free and pinned layers are denoted by m and p, respectively. The magnetization of the pinned layer points in the positive z-direction, p = +e z . The magnetization dynamics in the free layer is described by the LLG equation, where γ and α are the gyromagnetic ratio and Gilbert damping constant, respectively. The magnetic field consists of an applied field H appl and demagnetization field along the z-direction. Throughout this letter, the magnetic field is considered to poin...

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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.…”

mentioning

confidence: 99%

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

Kiselev

Sankey

Krivorotov

et al. 2003

Nature

1,948

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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Spin-current interaction with a monodomain magnetic body: A model study

Cited by 1,011 publications

References 9 publications

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact

Crossover between fast and slow excitation of magnetization by spin torque

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

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