Spectral Characteristics of the Microwave Emission by the Spin Hall Nano-Oscillator

Abstract

We utilized microwave spectroscopy to study the magnetization oscillations locally induced in a Permalloy film by a pure spin current, which is generated due to the spin Hall effect in an adjacent Pt layer. The oscillation frequency is lower than the ferromagnetic resonance of Permalloy, indicating that the oscillation forms a self-localized nonpropagating spin-wave soliton. At cryogenic temperatures, the spectral characteristics are remarkably similar to the traditional spin-torque nano-oscillators driven by spin-polarized currents. However, the linewidth of the oscillation increases exponentially with temperature and an additional peak appears in the spectrum below the ferromagnetic resonance, suggesting that the spectral characteristics are determined by interplay between two localized dynamical states.

Nanowire spin torque oscillator driven by spin orbit torques

“…The integrated power decreases with increasing T b and vanishes at T b E250 K. The actual temperature of the nanowire is significantly higher than T b due to Ohmic heating. The nanowire temperature can be estimated from measurements of the nanowire resistance as functions of T b and I dc 18 . As described in the Methods section, the actual nanowire temperature at I c and Figure 4c illustrates the temperature dependence of the nanowire STO spectral linewidth.…”

“…We apply a direct current bias I dc to the nanowire and measure the microwave signal emitted by the device using a spectrum analyzer 3 . The microwave signal V ac BI dc dR ac is generated by the AMR resistance oscillations dR ac arising from the magnetization self-oscillations 18 . Microwave signal emission, shown in Fig.…”

“…To estimate the actual temperature of the nanowire at large I dc , we compare measurements of the wire resistance as a function of temperature at small I dc ¼ 0.1 mA to measurements of the wire resistance versus I dc taken at the bath temperature T b ¼ 4.2 K (ref. 18). These data are plotted in Supplementary Fig.…”

“…ST oscillators (STO) have been realized in nanoscale spin valves 3,[5][6][7] , point contacts to magnetic multilayers [8][9][10] and nanoscale magnetic tunnel junctions [11][12][13][14][15] . Recently, a new type of STO based on current-induced spin orbit (SO) torques in a Permalloy(Py)/platinum(Pt) bilayer was demonstrated [16][17][18] . Spin orbit torques [19][20][21] in this system can arise from the spin Hall effect in Pt [22][23][24][25][26][27][28] and the Rashba effect at the Pt/Py interface [29][30][31][32] .…”

Current-induced spin torque resonance of a magnetic insulator

“…This makes them attractive for spintronics applications, such as torque-induced magnetization control in nanodevices [1][2][3], for sensing, data storage, interconnects, and logics. Up to now, however, most spin transfer torque studies focused on metallic ferromagnets [4][5][6][7][8], while magnetic insulators received much less attention [9][10][11]. However, some magnetic insulators such as yttrium iron garnet (YIG) with extremely low magnetization damping [12] are well suited for the long-range transmission of signals via magnetization dynamics, and may harbor magnon condensates [13] or magnonic crystals [14].…”