Spin-torque oscillator using a perpendicular polarizer and a planar free layer

Houssameddine, D.; Ebels, U.; Delaet, B.; Rodmacq, B.; Firastrau, I.; Ponthenier, F.; Brunet, Magali; Thirion, C.; Michel, Jean‐Philippe; Prejbeanu-Buda, L.; Cyrille, Marie-Claire; Redon, O.; Diény, B.

doi:10.1038/nmat1905

Cited by 557 publications

(391 citation statements)

References 34 publications

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“…The values of the parameters used in the above calculations are derived from typical experiments 8,11,14,15 . As shown in Fig.…”

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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“…The values of the parameters used in the above calculations are derived from typical experiments 8,11,14,15 . As shown in Fig.…”

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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“…25 presented analytical calculations using small free layer thickness of 4-5 nm, but they excluded this thickness from their micromagnetic simulations. Contrarily, the typical free layer thicknesses used in the experiments on nanopillars and nanocontacts [32][33][34][35][36][37][38][39] are around 4-5 nm. In the case of vortex state in nanopillars, microwave measurements, and micromagnetic simulations of the vortex gyrotropic motion excited by CPP are reported in Ref.…”

Section: Introductionmentioning

confidence: 99%

Limits for the vortex state spin torque oscillator in magnetic nanopillars: Micromagnetic simulations for a thin free layer

Aranda

González

Val

et al. 2010

Journal of Applied Physics

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Anomalous magnetic properties of 7nm single-crystal Co3O4 nanowires J. Appl. Phys. 111, 013910 (2012) High field-gradient dysprosium tips for magnetic resonance force microscopy Appl. Phys. Lett. 100, 013102 (2012) Dipolar interactions in magnetic nanowire aggregates J. Appl. Phys. 110, 123924 (2011) Dielectric and spin relaxation behaviour in DyFeO3 nanocrystals J. Appl. Phys. 110, 124301 (2011) Finite size versus surface effects on magnetic properties of antiferromagnetic particles Appl. Phys. Lett. 99, 232507 (2011) Additional information on J. Appl. Phys. We report micromagnetic simulations of magnetization dynamics of a vortex state in the free layer of a circular nanopillar excited by the spin transfer torque effect of a perpendicular to the layer ͑dot͒ plane spin-polarized electrical current. The magnetization of the reference layer ͑polarizer͒ is assumed to be fixed. A new regime of the dynamic magnetization response to the current is reported: vortex expelling from the dot, subsequent in-plane magnetization oscillations in single domain state, and the vortex return with an opposite core polarization. We analyze conditions ͑limits of the vortex state as a nano-oscillator͒ to achieve steady magnetization oscillations corresponding to a gyrotropic motion of the vortex core in terms of the current intensity. These conditions are formulated via the critical currents and vary greatly with the magnetic damping parameter and the cell size used for micromagnetic simulations. The existing experiments on the current induced magnetization dynamics in nanopillars and nanocontacts are discussed.

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“…Solving the Landau-Lifshitz-Gilbert equation, excitation of in-phase or antiphase synchronization, depending on the ways the oscillators are connected, is found. It is also found from both analytical and numerical calculations that the current-frequency relations for both parallel and series circuits are the same as that for a single spin-torque oscillator.Spin-torque oscillators have been a fascinating research target in the field of spintronics from the viewpoints of both nonlinear science and practical applications such as microwave generator and communication devices [1][2][3][4][5][6]. Above all, the exciting topic in this research field is the synchronization of spin-torque oscillators by the magnetic [7][8][9][10] and/or electrical [11][12][13][14][15] couplings.…”

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confidence: 99%

Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers

Taniguchi

Tsunegi

2017

Appl. Phys. Express

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A mutual synchronization of spin-torque oscillators coupled through current injection is studied theoretically. Models of electrical coupling in parallel and series circuits are proposed. Solving the Landau-Lifshitz-Gilbert equation, excitation of in-phase or antiphase synchronization, depending on the ways the oscillators are connected, is found. It is also found from both analytical and numerical calculations that the current-frequency relations for both parallel and series circuits are the same as that for a single spin-torque oscillator.Spin-torque oscillators have been a fascinating research target in the field of spintronics from the viewpoints of both nonlinear science and practical applications such as microwave generator and communication devices [1][2][3][4][5][6]. Above all, the exciting topic in this research field is the synchronization of spin-torque oscillators by the magnetic [7][8][9][10] and/or electrical [11][12][13][14][15] couplings. The synchronization of spin-torque oscillators results in an enhancement of the emission power and an increase of the quality factor of the practical devices. In addition, new applications such as brain-inspired computing based on the synchronized spin-torque oscillators are proposed very recently [16][17][18][19].An attractive structure of spin-torque oscillator for practical applications is that consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [20][21][22] because this type of spin-torque oscillator results in high emission power, narrow linewidth, and wide frequency tunability simultaneously. The oscillation properties of this type of spin-torque oscillator, such as the relation between the injected current and the oscillation frequency, as a single oscillator have been investigated both experimentally [22] and theoretically [23]. A possibility to excite a mutual synchronization in this type of spin-torque oscillators, however, has not been investigated yet.In this letter, a theoretical study on the mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers is presented. We focus on the coupling of spin-torque oscillators through the current injection, and develop models of the coupling in the parallel and series circuits. Solving the Landau-Lifshitz-Gilbert (LLG) equation numerically, we show that two spin-torque oscillators indicate in-phase or antiphase synchronization depending on the way the oscillators are connected. An analytical theory clarifying the relation between the current, oscillation frequency, and phase difference is also developed. Both the numerical and analytical calculations indicate that the dependence of oscillation frequency on the current for both the parallel and series circuits are identical to that of a single spin-torque oscillator.The system under consideration is schematically shown in Fig. 1. There are two spin-torque oscillators, and each oscillator consists of a free layer F k (k = 1, 2) and a pinned ...

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Spin-torque oscillator using a perpendicular polarizer and a planar free layer

Cited by 557 publications

References 34 publications

Crossover between fast and slow excitation of magnetization by spin torque

Crossover between fast and slow excitation of magnetization by spin torque

Limits for the vortex state spin torque oscillator in magnetic nanopillars: Micromagnetic simulations for a thin free layer

Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers

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