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

Sani, Sohrab R.; Persson, Johan; Mohseni, Seyed Majid; Pogoryelov, Yevgen; Muduli, P. K.; Eklund, Anders; Malm, Gunnar; Käll, Mikael; Dmitriev, Alexandre; Åkerman, Johan

doi:10.1038/ncomms3731

Cited by 113 publications

(91 citation statements)

References 52 publications

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“…The fabricated NC-STOs are based on a pseudo spin valve 11,35 with the layer structure Co (8 nm)/Cu (8 nm)/Py (4.5 nm), where the Co (fixed layer) acts as a relatively static current spinpolarizer whereas the Py (Ni 80 Fe 20 , free layer) is subject to STT induced magnetodynamics. Devices with both circular NCs and elliptical NCs with an aspect ratio r = 1.5 are defined via electron beam lithography.…”

Section: Disentangling Mode Coupling Mechanismsmentioning

confidence: 99%

Mode-coupling mechanisms in nanocontact spin-torque oscillators

et al. 2015

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Spin torque oscillators (STOs) are devices that allow for the excitation of a variety of magnetodynamical modes at the nanoscale. Depending on both external conditions and intrinsic magnetic properties, STOs can exhibit regimes of mode-hopping and even mode coexistence. Whereas modehopping has been extensively studied in STOs patterned as nanopillars, coexistence has been only recently observed for localized modes in nanocontact STOs (NC-STOs) where the current is confined to flow through a NC fabricated on an extended pseudo spin valve. By means of electrical characterization and a multi-mode STO theory, we investigate the physical origin of the mode coupling mechanisms favoring coexistence. Two coupling mechanisms are identified: (i) magnon mediated scattering and (ii) inter-mode interactions. These mechanisms can be physically disentangled by fabricating devices where the NCs have an elliptical cross-section. The generation power and linewidth from such devices are found to be in good qualitative agreement with the theoretical predictions, as well as provide evidence of the dominant mode coupling mechanisms.

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Section: Disentangling Mode Coupling Mechanismsmentioning

confidence: 99%

Mode-coupling mechanisms in nanocontact spin-torque oscillators

et al. 2015

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“…For example, in easyplane material based devices such as STNOs with Permalloy free layers, in addition to vortices [26][27][28], both propa-gating spin waves [29][30][31][32][33][34][35][36] and self-localized spin wave bullet solitons [31][32][33]37] can be generated experimentally.…”

Section: Introductionmentioning

confidence: 99%

Magnetic droplet solitons in orthogonal spin valves

Chung

Mohseni

Eklund

et al. 2015

Low Temperature Physics

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We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented. PACS: 75.30.Ds Spin waves;75.75.-c Magnetic properties of nanostructures.

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“…This mode has been shown to consist of exchange-dominated spin waves (SWs) propagating radially away from the NC region at frequencies above the ferromagnetic resonance (FMR) frequency with a wavenumber inversely proportional to the NC diameter. The propagating nature of this mode lends itself to coupling NC-STOs to achieve better spectral features by synchronization [19][20][21][22][23], to perform computation [24,25], or to propagate information in magnonic devices [26,27].…”

Section: Introductionmentioning

confidence: 99%

Propagating spin waves excited by spin-transfer torque: A combined electrical and optical study

et al. 2015

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Nanocontact spin-torque oscillators are devices in which the generation of propagating spin waves can be sustained by spin transfer torque. In the present paper, we perform combined electrical and optical measurements in a single experimental setup to systematically investigate the excitation of spin waves by a nanocontact spin-torque oscillator and their propagation in a Ni 80 Fe 20 extended layer. By using microfocused Brillouin light scattering we observe an anisotropic emission of spin waves, due to the broken symmetry imposed by the inhomogeneous Oersted field generated by the injected current. In particular, spin waves propagate on the side of the nanocontact where the Oersted field and the in-plane component of the applied magnetic field are antiparallel, while propagation is inhibited on the opposite side. Moreover, propagating spin waves are efficiently excited only in a limited frequency range corresponding to wavevectors inversely proportional to the size of the nanocontact. This frequency range obeys the dispersion relation for exchange-dominated spin waves in the far field, as confirmed by micromagnetic simulations of similar devices. The present results have direct consequences for spin wave based applications, such as synchronization, computation, and magnonics.

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

Cited by 113 publications

References 52 publications

Mode-coupling mechanisms in nanocontact spin-torque oscillators

Mode-coupling mechanisms in nanocontact spin-torque oscillators

Magnetic droplet solitons in orthogonal spin valves

Propagating spin waves excited by spin-transfer torque: A combined electrical and optical study

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