Noise-induced synchronization in spin torque nano oscillators

Nakada, Kazuyoshi; Yakata, S.; Kimura, Takashi

doi:10.1063/1.3680537

Cited by 33 publications

(26 citation statements)

References 10 publications

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“…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.…”

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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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mentioning

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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“…Here '+' sign represents the microwave power combiner [14,26]. (5) Common noise induced synchronization -electrically connected STNOs [25] (6) Common oscillating magnetic field-induced synchronization -electrically uncoupled [26,27].…”

Section: Synchronization In the Presence Of Oscillating Magnetic Fieldmentioning

confidence: 99%

Nonlinear dynamics of spin transfer nano-oscillators

2015

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The evolution equation of a ferromagnetic spin system described by Heisenberg nearest-neighbour interaction is given by Landau-Lifshitz-Gilbert (LLG) equation, which is a fascinating nonlinear dynamical system. For a nanomagnetic trilayer structure (spin valve or pillar) an additional torque term due to spin-polarized current has been suggested by Slonczewski, which gives rise to a rich variety of dynamics in the free layer. Under appropriate conditions the spin-polarized current gives a time-varying resistance to the magnetic structure thereby inducing magnetization oscillations of frequency which lies in the microwave region. Such a device is called a spin transfer nanooscillator (STNO). However, this interesting nanoscale level source of microwaves lacks efficiency due to its low emitting power typically of the order of nWs. To overcome this difficulty, one has to consider the collective dynamics of synchronized arrays/networks of STNOs as suggested by Fert and coworkers so that the power can be enhanced N 2 times that of a single STNO. We show that this goal can be achieved by applying a common microwave magnetic field to an array of STNOs. In order to make the system technically more feasible to practical level integration with CMOS circuits, we establish suitable electrical connections between the oscillators. Although the electrical connection makes the system more complex, the applied microwave magnetic field drives the system to synchronization in large regions of parameter space.

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“…However, an important issue with such devices regarding their practical realization is their low-output oscillation power and low spectral stability. A possible solution to these issues could be the synchronization of a few STNOs [6,19,21,22,26,28]. Synchronization among multiple auto-oscillators can also be useful in the framework of developing associative memories architectures [29][30][31][32].…”

Section: Introductionmentioning

confidence: 99%

“…Synchronization among multiple auto-oscillators can also be useful in the framework of developing associative memories architectures [29][30][31][32]. Previous studies reported on synchronization of STNOs interacting with others via spin waves [25,26,33], exchange coupling [6], electric currents [3,28,34], noisy current injection [19], or via magnetodipolar interaction [21,22,[35][36][37][38][39][40][41].…”

Section: Introductionmentioning

confidence: 99%

Optimizing magnetodipolar interactions for synchronizing vortex based spin-torque nano-oscillators

et al. 2015

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We report on a theoretical study of the magnetodipolar coupling and synchronization between two vortex-based spin-torque nano-oscillators (STVOs). In this work we study the dependence of the coupling efficiency on the relative magnetization parameters of the vortices in the system. This study is performed in order to propose an optimized configuration of the vortices for synchronizing STVOs. For this purpose, we combine micromagnetic simulations, the Thiele equation approach, and the analytical macrodipole approximation model to identify the optimized configuration for achieving phase-locking between neighboring oscillators. Notably, we compare vortices configurations with parallel (P) core polarities and with opposite (AP) core polarities. We demonstrate that the AP core configuration exhibits a coupling strength about three times higher than in the P core configuration.

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Noise-induced synchronization in spin torque nano oscillators

Cited by 33 publications

References 10 publications

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

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

Nonlinear dynamics of spin transfer nano-oscillators

Optimizing magnetodipolar interactions for synchronizing vortex based spin-torque nano-oscillators

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