Magnon Lifetimes on the Fe(110) Surface: The Role of Spin-Orbit Coupling

Abstract

We provide direct experimental evidence which demonstrates that, in the presence of a large spin-orbit coupling, the lifetime, amplitude, group, and phase velocity of the magnons propagating along two opposite (but crystallographically equivalent) directions perpendicular to the magnetization are different. A real time and space representation reveals that magnons with the same energy (eigenfrequency) propagate differently along two opposite directions. Our findings can inspire ideas for designing new spintronic devices.

Long-living terahertz magnons in ultrathin metallic ferromagnets

“…Figure 1d shows the intrinsic linewidth of the magnon excitation peak as a function of the wave vector. At the X-point, the wave vector of 1.15 Å À 1 , the linewidth is only 30 meV, which is smaller than the value observed for other metallic ferromagnets 13,14,29,31,32 . The lifetime of excitations can simply be obtained using the expression: t ¼ 2:/De, where : is reduced Planck constant and De is intrinsic linewidth, shown in Pd (001) substrate Comparing this data to the corresponding data of a two-atomic-layer-thick Fe film on W(110), one clearly observes that the lifetime in the FePd film is longer (see Fig.…”

“…The animated movie of the propagation is shown in Supplementary Movie 1. The lifetime of magnons in Fe films grown on W(110), at the wave vector of 0.5 Å À 1 , is only 37 fs (refs 13,14). The amplitude of the wave packet reduces to 1% already after 0.17 ps.…”

“…To extract the excitation energy and lifetime, the difference spectra were fitted using a convolution of a Gaussian and a Lorentzian function, in which the Gaussian represents the instrumental broadening and the Lorentzian represents the intrinsic lifetime broadening 13,14 . For a detailed description of the fitting procedure, see Supplementary Note 1 and Supplementary Figure 1.…”

“…As a result, the terahertz magnons in metallic ferromagnets feature a very short lifetime, only up to a few tens of femtoseconds 5,[11][12][13][14]17 . The decay of magnons into Stoner excitations is usually referred to as Landau damping.…”

“…This means that the use of high-frequency (terahertz) magnons would provide a great opportunity for the design of ultrafast devices. However, one of the main challenges for using terahertz magnons is their short lifetime in metallic ferromagnets [5][6][7][8][9][10][11][12][13][14][15][16] . Hence, the discovery of a low-damping material would push the progress in the field of terahertz magnonics one big step further.…”