Magnetization switching by current and microwaves

Taniguchi, Tomohiro; Saida, Daisuke; Nakatani, Yoshinobu

doi:10.1103/physrevb.93.014430

Cited by 34 publications

(59 citation statements)

References 87 publications

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“…The absence of the self-oscillation indicates that the threshold current density is larger than the current necessary to stabilize the self-oscillation. This dynamics is consistent with our previous work 16 .…”

Section: Pacs Numberssupporting

confidence: 94%

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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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Section: Pacs Numberssupporting

confidence: 94%

“…Positive current corresponds to electron flow from the free to the pinned layer. The values of the parameters Note that the parameter λ has often been assumed to be zero in previous works [9][10][11]13,17 , including our recent work 16 , for simplicity. However, this parameter plays a key role, as described in the following discussion.…”

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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“…Numerical simulation and analytical analysis To understand these behaviors of the magnetization and find a way to obtain OPP stable oscillation in the general case of LFM  tFM, we analytically solve the time evolution of the energy of the magnetization [19,20]. In the following derivation, we consider the case of x N < z N (tFM < LFM) without the loss of generality.…”

Section: Device Structuresmentioning

confidence: 99%

“…Because p = k and β = 1 are held on the saddle energy curve, the integration of Eq. (19), (20) and (21)…”

Section: Supplementary Informationmentioning

confidence: 99%

Bias-field-free spin Hall nano-oscillators with an out-of-plane precession mode

Shirokura

Hai

2020

Journal of Applied Physics

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Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave oscillators with high durability due to a small driving current. However, conventional SHNOs with an in-plane precession (IPP) mode require a bias field for stable oscillations which is not favored in certain applications such as neuromorphic computing. Here, we propose and theoretically analyze a bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession (OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically and numerically. We derive formulas for driving currents and precession frequency, and show that they are in good agreement with numerical simulation results. We show that our proposed SHNOs can be driven by much smaller bias current than conventional spin torque nano-oscillators.

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“…[31], the critical and switching current densities are defined as j c = lim E→Emin j(E) and j sw = max[j(E)], respectively, which are not necessarily same. The analytical solution of j(E) for an arbitrary E is complex.…”

Section: Llg Equationmentioning

confidence: 99%

Current-Induced Instability of a Perpendicular Ferromagnet in Spin Hall Geometry

2016

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Abstract-We develop a theoretical formula of spin Hall torque in the presence of two ferromagnets. While the direction of the conventional spin Hall torque always points to the in-plane direction, the present system enables to manipulate the torque direction acting on one magnetization by changing the direction of another magnetization. Based on the diffusion equation of the spin accumulation and the Landauer formula, we derive analytical formula of the spin Hall torque. The present model provides a solution to switch a perpendicular ferromagnet deterministically at zero field using the spin Hall effect.Index Terms-spintronics, spin Hall effect, perpendicularly magnetized free layer

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Magnetization switching by current and microwaves

Cited by 34 publications

References 87 publications

Crossover between fast and slow excitation of magnetization by spin torque

Crossover between fast and slow excitation of magnetization by spin torque

Bias-field-free spin Hall nano-oscillators with an out-of-plane precession mode

Current-Induced Instability of a Perpendicular Ferromagnet in Spin Hall Geometry

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