Full Control of the Spin-Wave Damping in a Magnetic Insulator Using Spin-Orbit Torque

Abstract

It is demonstrated that the threshold current for damping compensation can be reached in a 5 μm diameter YIG(20 nm)|Pt(7 nm) disk. The demonstration rests upon the measurement of the ferromagnetic resonance linewidth as a function of I(dc) using a magnetic resonance force microscope (MRFM). It is shown that the magnetic losses of spin-wave modes existing in the magnetic insulator can be reduced or enhanced by at least a factor of 5 depending on the polarity and intensity of an in-plane dc current I(dc) flowing through the adjacent normal metal with strong spin-orbit interaction. Complete compensation of the damping of the fundamental mode by spin-orbit torque is reached for a current density of ∼3×10(11) A·m(-2), in agreement with theoretical predictions. At this critical threshold the MRFM detects a small change of static magnetization, a behavior consistent with the onset of an auto-oscillation regime.

Current-induced spin torque resonance of a magnetic insulator

“…Magnetic insulators in particular can be engineered for low saturation magnetization [39], further increasing the effectiveness of spin transfer torque mediated magnetization actuation. Recent results [10,11] also indicate that the spin transfer torque may be able to couple to the Néel order parameter in antiferromagnetic insulators which could allow for very high-frequency dynamics. The origin of the phase offset δ is not known.…”

“…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].…”

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

“…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.…”

“…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.…”

Spin waves in ferromagnetic insulators coupled via a normal metal

“…[8][9][10][11][12][13][14][15][16][17][18][19] In ferromagnetic insulators, currentinduced spin-transfer torques from a neighboring normal metal (NM) that exhibits out-of-equilibrium spin accumulation may manipulate the magnetization of the insulator and excite spin waves. 8,20,21 The out-of-equilibrium spin accumulation of the normal metal may be induced via the spin Hall effect or by currents passing through other adjacent conducting ferromagnets. Conversely, excited spin waves pump spins into adjacent NMs, and this spin current may be measured in terms of the inverse spin Hall voltages or by other conducting ferromagnets.…”