Impact of the electrical connection of spin transfer nano-oscillators on their synchronization: an analytical study

Georges, B.; Grollier, Julie; Cros, Vincent; Fert, A.

doi:10.1063/1.2945636

Cited by 108 publications

(79 citation statements)

References 21 publications

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“…In the parallel electrical connection of the multi-nanocontacts in our devices, the power delivered to the 50-O measurement load by N individually oscillating nanocontacts is expected to drop as N À 2 due to the other nanocontacts acting as shunts 50 (see also Supplementary Note 1). When comparing the typical nonsynchronized power of one through five-nanocontact STOs in Figs 4 and 5, we clearly observe a dramatic reduction in power with the number of nanocontacts.…”

Section: Discussionmentioning

confidence: 99%

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

et al. 2013

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Spin-torque oscillators offer a unique combination of nanosize, ultrafast modulation rates and ultrawide band signal generation from 100 MHz to close to 100 GHz. However, their low output power and large phase noise still limit their applicability to fundamental studies of spin-transfer torque and magnetodynamic phenomena. A possible solution to both problems is the spin-wave-mediated mutual synchronization of multiple spin-torque oscillators through a shared excited ferromagnetic layer. To date, synchronization of high-frequency spin-torque oscillators has only been achieved for two nanocontacts. As fabrication using expensive top-down lithography processes is not readily available to many groups, attempts to synchronize a large number of nanocontacts have been all but abandoned. Here we present an alternative, simple and cost-effective bottom-up method to realize large ensembles of synchronized nanocontact spin-torque oscillators. We demonstrate mutual synchronization of three high-frequency nanocontact spin-torque oscillators and pairwise synchronization in devices with four and five nanocontacts.

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Section: Discussionmentioning

confidence: 99%

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

et al. 2013

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“…The mutual, as well as self, synchronization of the spin torque induced magnetization oscillation by using spin waves, electric current, microwave field, or dipole coupling has been an exciting topic from the viewpoints of both nonlinear science and practical applications [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] . The key quantity of the synchronization is the phase difference ∆ϕ between each magnetization to enhance the emission power from the spin torque oscillators and to investigate new practical applications such as neuromorphic architectures 38,39 .…”

Section: A Transverse Geometrymentioning

confidence: 99%

Dynamic coupling of ferromagnets via spin Hall magnetoresistance

Taniguchi

2017

Phys. Rev. B

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The synchronized magnetization dynamics in ferromagnets on a nonmagnetic heavy metal caused by the spin Hall effect is investigated theoretically. The direct and inverse spin Hall effects near the ferromagnetic/nonmagnetic interface generate longitudinal and transverse electric currents. The phenomenon is known as the spin Hall magnetoresistance effect, whose magnitude depends on the magnetization direction in the ferromagnet due to the spin transfer effect. When another ferromagnet is placed onto the same nonmagnet, these currents are again converted to the spin current by the spin Hall effect and excite the spin torque to this additional ferromagnet, resulting in the excitation of the coupled motions of the magnetizations. The in-phase or antiphase synchronization of the magnetization oscillations, depending on the value of the Gilbert damping constant and the field-like torque strength, is found in the transverse geometry by solving the Landau-Lifshitz-Gilbert equation numerically. On the other hand, in addition to these synchronizations, the synchronization having a phase difference of a quarter of a period is also found in the longitudinal geometry. The analytical theory clarifying the relation among the current, frequency, and phase difference is also developed, where it is shown that the phase differences observed in the numerical simulations correspond to that giving the fixed points of the energy supplied by the coupling torque.

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“…Here, = ( ) is the vortex core position, is the gyrovector, ̂ is the damping, is the potential energy of the vortex, is the spin-transfer force and is the dc current applied to oscillator i. The total microwave current flowing through the oscillators consists of the external microwave current provided by the source, as well as the microwave currents emitted by the oscillators themselves (see Supplementary Material [32] for details) [33].…”

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confidence: 99%

Enhancing the injection locking range of spin torque oscillators through mutual coupling

Romera

Talatchian

Lebrun

et al. 2016

Applied Physics Letters

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We investigate how the ability of the vortex oscillation mode of a spin-torque nanooscillator to lock to an external microwave signal is modified when it is coupled to another oscillator. We show experimentally that mutual electrical coupling can lead to locking range enhancements of a factor 1. 64. Furthermore, we analyze the evolution of the locking range as a function of the coupling strength through experiments and numerical simulations. By uncovering the mechanisms at stake in the locking range enhancement, our results will be useful for designing spin-torque nano-oscillators arrays with high sensitivities to external microwave stimuli.Spin-torque nano-oscillators (STNOs) are promising candidates for the next generation of multifunctional spintronic nano-devices [1] such as efficient integrated microwave generators [2] and detectors [3,4]. One of their characteristic features compared to other auto-oscillators is their high non-linearity [5]. On one hand, this high nonlinearity translates into one of their most attractive properties: their ability to easily adapt their frequencies to external stimuli. On the other hand, by increasing their sensitivity to noise, it has the undesirable effect of broadening the spectral linewidth. In the last few years, many efforts have been made to improve the spectral purity of spintorque oscillators, a crucial step towards most applications. From these studies, a promising approach consists in the synchronization of the oscillators to an external microwave source [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] (injection locking), or to other oscillators [21][22][23][24][25][26][27] (mutual synchronization). In both cases, a crucial parameter to optimize for applications is the locking range, which should be as large as possible. A first way to increase the locking range is to work in regimes where the oscillator's nonlinearity is the largest. However, as mentioned earlier, this comes at the detriment of spectral purity. In the case of injection locking, another possibility is to increase the power of the external signal, but this is limited by the breakdown voltage of the tunnel barrier of the device and results in an increase of power consumption. Therefore, finding alternative paths to enhance the locking range is an important step towards designing next generation's magnetic microwave devices.In this manuscript we combine experimental results with numerical simulations to show that the injection locking range of a spin-torque oscillator can be enhanced by coupling it to another spintorque oscillator. Furthermore, it is shown that the locking range can be tuned by changing the mutual coupling strength between oscillators. (7) is the free layer and numbers represent thickness in nanometers. Samples were grown by sputterdeposition and patterned down to the bottom electrode into circular nanopillars with a diameter of 200 nm. The nano-pillars exhibit a TMR of 64% and a resistance-area product of RA~1 Ω.μm 2 . With this combination of materials and geometry, th...

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Impact of the electrical connection of spin transfer nano-oscillators on their synchronization: an analytical study

Cited by 108 publications

References 21 publications

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

Dynamic coupling of ferromagnets via spin Hall magnetoresistance

Enhancing the injection locking range of spin torque oscillators through mutual coupling

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