Microwave generation by spin Hall nanooscillators with nanopatterned spin injector

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

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

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

Mazraati

Chung

Houshang

et al. 2016

“…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.…”

mentioning

confidence: 99%

Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators

Langenfeld

Tshitoyan

Fang

et al. 2016

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...

“…This spin-Hall torque can counteract damping in the ferromagnet and has been shown to switch uniform magnetization, 6-9 drive domain walls, [10][11][12] and control precessional magnetization dynamics. 7,9,[13][14][15][16][17][18][19][20][21][22][23] Despite the demonstrated utility of the spin Hall effect, there exists a wide disparity in its reported magnitude parameterized by the spin Hall angle. For example, reported spin…”

mentioning

confidence: 99%

Quantification of the spin-Hall anti-damping torque with a resonance spectrometer

Emori

Nan

Oxholm

et al. 2015

We present a simple technique using a cavity-based resonance spectrometer to quantify the anti-damping torque due to the spin Hall effect. Modification of ferromagnetic resonance is observed as a function of small DC current in sub-mm-wide strips of bilayers, consisting of magnetically soft FeGaB and strong spin-Hall metal Ta. From the detected current-induced linewidth change, we obtain an effective spin Hall angle of 0.08-0.09 independent of the magnetic layer thickness. Our results demonstrate that a sensitive resonance spectrometer can be a general tool to investigate spin Hall effects in various material systems, even those with vanishingly low conductivity and magnetoresistance.