A 20 nm spin Hall nano-oscillator

Abstract

Spin Hall nano-oscillators (SHNOs) are an emerging class of pure spin current driven microwave signal generators. Through the fabrication of 20 nm nano-constrictions in Pt/NiFe bilayers, we demonstrate that SHNOs can be scaled down to truly nanoscopic dimensions, with the added benefit of ultra-low operating currents and improved power conversion efficiency. The lateral confinement leads to a strong shape anisotropy field as well as an additional demagnetizing field whose reduction with increasing auto-oscillation amplitude can yield a positive current tunability contrary to the negative tunability commonly observed for localized excitations in extended magnetic layers. Micromagnetic simulations corroborate the experimental findings and suggest that the active magnetodynamic area resides up to 100 nm outside of the nano-constriction.

Auto-oscillating Spin-Wave Modes of Constriction-Based Spin Hall Nano-oscillators in Weak In-Plane Fields

“…Nanoscale, spin current driven [1][2][3], auto-oscillators [4][5][6][7][8][9][10][11] are of great interest both for ultra-wideband microwave signal generation [12,13] and detection [14], and for neuromorphic computing [15][16][17]. A recent subset of these oscillators, so-called spin Hall nano-oscillators (SHNOs) [18][19][20][21][22][23][24][25][26][27][28][29], are driven by pure spin currents injected from an adjacent layer with strong spin-orbit coupling, such as Pt or W, and have demonstrated highly tunable microwave signals at room temperature with frequencies up to 28 GHz [30].…”

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

“…Spin Hall nano-oscillators [4][5][6][7][8] (SHNOs) rely on SOT to overcome the local spin wave damping and sustain steady-state, current-and field-tunable, precession of the magnetization around an effective magnetic field. SHNOs have been demonstrated using different FM/NM combinations such as NiFe/Pt 5,7,9,10 , NiFe/W 6 , Co 40 Fe 40 B 20 /Pt 11 and YIG/Pt 12 . Finding materials with a high charge-to-spin current conversion, quantified by the spin Hall angle (θ SH = J s /J c ), has been of particular interest, with Pt, Ta 3 , W 6 , AuTa 13 , and CuBi 14 being prominent examples.…”

Magnetic droplet solitons generated by pure spin currents

“…However, because of the strongly localized injection of spin current in these devices, the solitons were found to be pinned in the active device area, similarly to the conventional NC-STNOs. Another type of SHE nanooscillators that received a significant attention due to their simplicity, geometric flexibility, and efficient operation, are based on a magnetic nanoconstriction [27,[30][31][32]. These devices have been recently utilized to demonstrate 4 SHE-driven magnetization auto-oscillations in magnetic films with PMA [32].…”

“…Over the last few years, a variety of SHE-based STT devices with novel geometries and functionalities have been demonstrated [24]. In particular, it was shown that magnetization dynamics can be excited by SHE [25,26], which led to the development of nanooscillators driven by pure spin currents, which are characterized by moderate heat generation, high oscillation coherence, and efficient tunability of the oscillation frequency [27][28][29][30][31][32][33].…”