CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability

Zahedinejad, Mohammad; Mazraati, Hamid; Fulara, Himanshu; Yue, Jin; Jiang, Sheng; Awad, Ahmad A.; Åkerman, Johan

doi:10.1063/1.5022049

Cited by 66 publications

(56 citation statements)

References 32 publications

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“…14 For most of these applications, the SHNO performance needs to be enhanced to offer low threshold currents (low power consumption), high microwave output power, and low linewidth. While it has been shown that the synchronization of two or more SHNOs can be used to improve the power and coherency of the generated microwave signal, [15][16][17] several studies have also focused on enhancing the efficiency of spin current generation by using other heavy metals with higher n SH , such as b-W, [18][19][20] b-Ta, 21 and V. 22 Compared to Pt, these materials typically suffer from excessive heating due to their higher resistivity, which can be problematic when a large number of them are placed together in a small area to operate collectively, increasing the proportion of the current going through the ferromagnetic layer.…”

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Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting

Mazraati

Zahedinejad

Åkerman

2018

Applied Physics Letters

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We investigate the effect of hafnium (Hf) dusting on the magnetodynamical properties of NiFe/Pt bilayers using spin-torque-induced ferromagnetic resonance measurements on 6 lm wide microstrips on high-resistive Si substrates. Based on two series of NiFe(t NiFe)/Hf(t Hf)/Pt(5) stacks, we first demonstrate that the zero-current magnetodynamic properties of the devices benefit from Hf dusting: (i) the effective magnetization of the NiFe layer increases by 4%-8% with Hf present and (ii) the damping a decreases linearly with t Hf by up to 40%. The weaker anisotropic magnetoresistance (AMR ' 0.3%-0.4%) of the 3 nm NiFe series is largely unaffected by the Hf, while the stronger AMR of the 5 nm NiFe series drops from 0.7% to 0.43% with increasing t Hf. We find that the spin Hall efficiency n SH is independent of the NiFe thickness, remaining unaffected (n SH ¼ 0.115) up to t Hf ¼ 0.4 nm and then decreasing linearly for higher t Hf. The different trends of a and n SH suggest that there is an optimum Hf thickness ('0.4 nm) for which the threshold current for auto-oscillation should have a minimum, while the much lower damping should improve mutual synchronization. Our results also indicate that the spin-orbit torque is entirely damping-like with no field-like torque component. Finally, the internal spin Hall angle of Pt is estimated to be h SH ¼ 0.22 by calculating the transparency of the interface.

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Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting

Mazraati

Zahedinejad

Åkerman

2018

Applied Physics Letters

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“…In certain materials (e.g. Pt [13], Ta [27] and W [28], [29]), the conversion ratio from charge to spin current, called spin-Hall angle (SHA) is large enough to exert a sufficient torque on an adjacent FL to excite magnetization precession. The three-terminal MTJ-SHNO architecture proposed in [16] is based on these principles where a Ta strip is providing spin injection into the FL.…”

Section: A Basic Operation Of Three-terminal Mtj-shnos With Vcmamentioning

confidence: 99%

Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators

et al. 2019

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“…In AMR, the resistance of the material is at a maximum when the current and magnetization are in a parallel configuration, and at a minimum when perpendicular. For a typical thin ferromagnetic layer, the AMR value is less than 1% at room temperature [55]; however, in emerging semimetal topological materials, it can reach a few hundred percent [56]. The resistivity can then be described through the angular dependency:…”

Section: Theoretical Background 1anisotropic Magnetoresistancementioning

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Current Modulation of Nanoconstriction Spin-Hall Nano-Oscillators

et al. 2017

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This thesis explores the vibrant phenomena of spin Hall nano-oscillators (SHNOs); from wideband oscillation at the GHz range, through propagating spin-wave emission, to mutual synchronization in two-dimensional SHNO arrays, and tries to lay the foundation for a far-reaching SHNO technology, targeting magnonics, microwave signal generation, and neuromorphic computing. After a short introduction to the theoretical background in Chapter 1, in Chapter 2, ways of improving the spin transport properties between NiFe and Pt are explored: an 0.4 nm ultra-thin layer of Hf at the NiFe/Pt interface is found to reduce the threshold current by 20% as a result of the change in spin mixing conductance G Ö eff. Then, W/CoFeB/MgO stacks with perpendicular magnetic anisotropy (PMA) are used to demonstrate wide frequency tunability and sub-mA threshold currents in CMOS compatible SHNOs. By further increasing the PMA, the auto-oscillation frequency exceeds the ferromagnetic resonance (FMR) frequency, turning the SHNO into a propagating spin-wave emitter in which the propagation wave-vector is tunable with applied current and field. Finally, a GHz nano-scale SHNO modulated by an 80 MHz radio-frequency (RF) current is presented. The modulation needs no bulky microwave mixer, promising a compact modulator unit. Chapter 3 introduces two-dimensional SHNO arrays. Robust mutual synchronization is demonstrated in arrays accommodating up to 64 oscillators, achieving record high quality factors of 170,000 at an operating frequency of 10 GHz. Injection of two external microwave signals reproduces the two-dimensional synchronization maps used in neuromorphic vowel recognition. Chapter 4 emphasizes the importance of individual SHNO control in arrays. Gated SHNOs are demonstrated with substantial voltage tuning of the threshold current and the SHNO frequency. Voltage controlled mutual synchronization is also demonstrated. The MgO/AlO x /Si 3 N 4 gate is found to exhibit a memristive behavior governed by ion migration and acts as an embedded memory making each SHNO a complete non-volatile oscillator with integrated weights. The exciting nature of coupled non-volatile oscillator arrays controlled by electric field could lead to a paradigm shift in non-conventional computing. Chapter 5 discusses the implications of the demonstrated SHNO technology and how it may impact future applications.

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CMOS compatible W/CoFeB/MgO spin Hall nano-oscillators with wide frequency tunability

Cited by 66 publications

References 32 publications

Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting

Improving the magnetodynamical properties of NiFe/Pt bilayers through Hf dusting

Compact Macrospin-Based Model of Three-Terminal Spin-Hall Nano Oscillators

Current Modulation of Nanoconstriction Spin-Hall Nano-Oscillators

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