We investigate the effect of an electrical current on the attenuation length of a 900 nm wavelength spin-wave in a permalloy/Pt bilayer using propagating spin-wave spectroscopy. The modification of the spin-wave relaxation rate is linear in current density, reaching up to 14% for a current density of 2.3 × 1011 A/m2 in Pt. This change is attributed to the spin transfer torque induced by the spin Hall effect and corresponds to an effective spin Hall angle of 0.13, which is among the highest values reported so far. The spin Hall effect thus appears as an efficient way of amplifying/attenuating propagating spin waves.
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Strictly speaking, the odd part of the frequency shift also contains a contribution from the current-induced spin-wave Doppler shift. This contribution can be extracted easily by comparing the frequency shifts measured for two counter-propagating spin waves for a given current direction.29 The Doppler shift extracted for an applied current of 50 mA is of the order of 9 MHz, which is much lower than the 110 MHz Oersted field contribution. As a consequence, the Doppler effect has been neglected in our analysis.
The magnetization decrease is obtained by differentiating the Damon-Eshbach dispersion relation with respect to . The corresponding temperature increase may be estimated from the variation deduced from SQUID measurements of permalloy films with similar thickness. A very similar temperature increase is estimated by monitoring the resistance of the strip, which varies from 31.4 Ω at small current to 39.5 Ω at mA, and by using an average temperature coefficient of for the bilayer resistance.
Given its very small amplitude of (at most) 1 mT, the Oersted field is not expected to affect and significantly, contrary to Joule heating.
