Nanoconstriction-based spin-Hall nano-oscillator

Demidov, V. E.; Urazhdin, Sergei; Zholud, Andrei; Садовников, А. В.; Demokritov, S. O.

doi:10.1063/1.4901027

Cited by 187 publications

(147 citation statements)

References 21 publications

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“…To date, most SHNOs have been based on NiFe/ Pt, 2,[13][14][15][16][17][18][19][20] YIG/Pt, 21,22 and CoFeB/Pt, 23 with SOT produced by a Pt layer. Many other heavy metals, such as W, 10,11 IrCu, 24,25 and CuBi, 26 have however been investigated, revealing that the so-called spin Hall angle (h SH ), which describes the charge current to spin current conversion efficiency, can exceed that of Pt.…”

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confidence: 99%

“…Figure 5 shows that I th depends linearly on the nano-constriction width, and the values observed are more than 60% lower than those from previous reports on Pt-based SHNOs. 2,13,14,[16][17][18]21,23 The effective threshold current flowing through the W layer, shown on the right-hand y-axis of Figure 5, can be calculated by considering the ratio of the Py and W resistivities. This shows that a current of only about 75 lA in W can excite Py auto-oscillations in a 80 nm nano-constriction.…”

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confidence: 99%

“…We find a large negative value of h SH ¼ À0.385 and a corresponding dramatic reduction of the SHNO threshold current by over 60% compared to Pt-based SHNOs. 2,[13][14][15][16][17][18][19][21][22][23] All thin films were deposited at room temperature on cplane sapphire substrates using magnetron sputtering in a 2.5 mTorr Ar atmosphere, in an ultra-high vacuum (base pressure below 1 Â 10 À8 mTorr) AJA Orion 8 sputtering system. First we carried out a detailed study of the thickness dependence of the W film resistivity in films deposited at a rate of 0.07 Å /s.…”

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confidence: 99%

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Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

Mazraati

Chung

Houshang

et al. 2016

Applied Physics Letters

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Low operational current spin Hall nano-oscillators based on NiFe/W bilayers. Letters, 109(24) We demonstrate highly efficient spin Hall nano-oscillators (SHNOs) based on NiFe/b-W bilayers. Thanks to the very high spin Hall angle of b-W, we achieve more than a 60% reduction in the autooscillation threshold current compared to NiFe/Pt bilayers. The structural, electrical, and magnetic properties of the bilayers, as well as the microwave signal generation properties of the SHNOs, have been studied in detail. Our results provide a promising path for the realization of low-current SHNO microwave devices with highly efficient spin-orbit torque from b-W. Published by AIP Publishing. Applied Physics

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Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

Mazraati

Chung

Houshang

et al. 2016

Applied Physics Letters

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“…The combination of the spin-Hall effect and the spintransfer torque may be used to compensate the magnetic damping of a ferromagnet, facilitating precession of the macroscopic magnetization by the application of a direct current [1][2][3][4][5] . Such a device, a spin-Hall oscillator, is patterned in a simple current in-plane geometry and contains no tunnel barriers.…”

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confidence: 99%

Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators

Langenfeld

Tshitoyan

Fang

et al. 2016

Applied Physics Letters

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We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators.The combination of the spin-Hall effect and the spintransfer torque may be used to compensate the magnetic damping of a ferromagnet, facilitating precession of the macroscopic magnetization by the application of a direct current 1-5 . Such a device, a spin-Hall oscillator, is patterned in a simple current in-plane geometry and contains no tunnel barriers. The ability of the spin-Hall effect to apply a spin-current transverse to the chargecurrent enables the use of conducting magnetic materials as well as low-damping, insulating materials like yttriumiron-garnet (YIG) 5 . This is in contrast to conventional spin-torque nano-oscillators where a spin-polarized current is passed into a conducting ferromagnetic layer 6 . Despite being attractive due to their geometric simplicity and flexibility in choice of magnetic materials, for spin-Hall oscillators to become competitive with conventional spin-torque nano-oscillators, sources of damping such as spin-pumping 7 and multi-magnon scattering via exchange magnons 8,9 should be addressed in order to reduce the linewidth and increase the power generation efficiency. In this Letter we show that the current induced excitation of incoherent exchange magnons can be observed using a direct current measurement. We find a change in the sample resistance which correlates with the reduction of saturation magnetization taken from our spectroscopy measurements, similar to previously reported results 9 . Both phenomena are consistent within a simple model only utilizing the precession cone-angle of the auto-oscillatory exchange magnons.The sample is a Pt(3)/Py(4)/AlO x (1.6) trilayer deposited by d.c. magnetron sputtering onto a MgO substrate. Numbers in parentheses give thicknesses in nanometers. The multilayer is patterned into a 500 nm × 6 µm bar via electron-beam lithography and subsequent Ar ion milling. Adjacent evaporated Cr(5)/Au(50) pads a) current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany b) ajf1006@cam.ac.uk serve as contact pads. When current is applied to this structure, the portion of the current flowing inside the heavy metal (platinum) generates an out-of-plane spincurrent via the spin-Hall effect (SHE). This spin-current exerts a spin-transfer torque (STT) on the magnetization of the ferromagnetic layer (permalloy) 10,11 , which can oppose the magnetic damping, leading to a change in the Gilbert damping parameter α 12,13 :Here, α 0 is the pristine damping parameter, j c,hm is the charge-curren...

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“…Spin-Hall driven auto-oscillation of the quasi-uniform mode in an extended ferromagnetic film with uniformly applied spin-torque has been hampered by nonlinear magnon scattering processes that redistribute energy from the desired mode into a large number of degenerate spin wave modes [6]. Spin-Hall oscillators demonstrated to date have utilized either local, nanoscale excitation of a mode whose resonance frequency lies below the continuous spin wave dispersion of the extended FM film [2,[7][8][9], or have geometrically confined the excited mode (in, e.g., a nanowire) so that the degeneracies of the spin wave dispersion are strongly lifted [3,10,11]. The ability to engineer the magnon spectrum could permit systematic tuning of multi-mode interactions and detailed study of their implications for spin-Hall oscillators.…”

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confidence: 99%

Engineering the Spectrum of Dipole Field-Localized Spin-Wave Modes to Enable Spin-Torque Antidamping

Zhang

Manuilov

et al. 2017

Phys. Rev. Applied

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Auto-oscillation of a ferromagnet due to spin-orbit torques in response to a dc current is of wide interest as a flexible mechanism for generating controllable high frequency magnetic dynamics. However, spin wave mode degeneracies and nonlinear magnon-magnon scattering impede coherent precession. Discretization of the spin wave modes can reduce this scattering. Spatial localization of the spin wave modes by the strongly inhomogeneous dipole magnetic field of a nearby spherical micromagnet provides variable spatial confinement, thus offering the option of systematic tunability of magnon spectrum for studying multi-mode interactions. Here we demonstrate that field localization generates a discrete spin wave mode spectrum observable as a series of well-resolved localized modes in the presence of imposed spin currents arising from the spin Hall effect (SHE) in a permalloy/platinum (Py/Pt) microstrip. The observation of linewidth reduction through damping control in this micromagnetically engineered spectrum demonstrates that localized modes can be controlled efficiently, an important step toward continuously tunable SHE driven auto-oscillators.

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Nanoconstriction-based spin-Hall nano-oscillator

Cited by 187 publications

References 21 publications

Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

Low operational current spin Hall nano-oscillators based on NiFe/W bilayers

Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators

Engineering the Spectrum of Dipole Field-Localized Spin-Wave Modes to Enable Spin-Torque Antidamping

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