Differences in the magnon diffusion length for electrically and thermally driven magnon currents in Y3Fe5O12

Abstract

Recent demonstration of efficient transport and manipulation of spin information by magnon currents have opened exciting prospects for processing information in devices. Magnon currents can be excited both electrically and thermally, even in magnetic insulators, by applying charge currents in an adjacent metal layer. Earlier reports in thin yttrium iron garnet (YIG) films suggested that the diffusion length of magnons is independent on the excitation method, but different values were obtained in thicker films.Here, we study the magnon diffusion length for electrically and thermally excited magnons in a 2-m-thick YIG film as a function of temperature and magnetic field. Our results evidence that the diffusion length depends on the generation mechanism, suggesting that magnons of different energies are excited -sub-thermal and thermal magnons for electrically and thermally driven magnon currents, respectively-and, consequently, indicating that the magnon diffusivity is frequency dependent. Moreover, we show that the damping of the thermally driven magnons with magnetic field is weaker than for those excited electrically. Finally, we demonstrate that the magnon diffusion length for thermally excited magnons is independent of the YIG thickness and material growth conditions, confirming that this quantity is an intrinsic parameter of YIG.

Anisotropic Magnon Spin Transport in Ultra-thin Spinel Ferrite Thin Films -- Evidence for Anisotropy in Exchange Stiffness

“…We For both λ 1ω and λ 2ω we observe significantly larger (> 30%) spin diffusion lengths along the <110> family of axes (easy axes) compared to the <100> axes (hard axes). We also find that the extracted values of λ 2ω are slightly larger than λ 1ω , which has also been observed previously for YIG thin films [20]. This difference can be explained as due to the different mechanisms by which the nonequilibrium magnon distributions are generated for the two signals.…”

“…Magnon spin transport has been demonstrated experimentally in both insulating ferrimagnets [2][3][4][5][6][7][8][9][10][11][12][13][14] and antiferromagnets [15][16][17]. The magnon spin diffusion length, the characteristic propagation length, has been studied under various conditions of temperature [11,[18][19][20], magnon chemical potential [21][22][23], and external magnetic field [11,20,24]. Previous measurements on ferrimagnetic insulators have focused on yttrium iron garnet (YIG), either with thick films (>100 nm) which are fully relaxed relative to the substrate [3,5,20] or with thinner films [25].…”

“…The magnon spin diffusion length, the characteristic propagation length, has been studied under various conditions of temperature [11,[18][19][20], magnon chemical potential [21][22][23], and external magnetic field [11,20,24]. Previous measurements on ferrimagnetic insulators have focused on yttrium iron garnet (YIG), either with thick films (>100 nm) which are fully relaxed relative to the substrate [3,5,20] or with thinner films [25]. In either case, YIG has very weak magnetic anisotropy, and no anisotropies have been observed in the spin transport.…”

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…Thus, a full quantitative understanding of all signal contributions for the thermal part is very challenging and different results have been observed in the experiment. [67,161,162] Up to now, we only accounted for the electrical injection and detection mechanisms in the NM to explain the all-electrical magnon transport experiments. As the injected pure spin current is transported via magnons in the MOI, we also have to account for the magnon transport properties; the following discussion is based on a more detailed description of magnon transport in various studies.…”

Giant magnon spin conductivity approaching the two-dimensional transport regime in ultrathin yttrium iron garnet films

“…We modulate the AC current I by a low frequency (18 Hz) and detect the first/second harmonic signal V nl (ω)/V nl (2ω) by lockin amplifiers (see Methods). V nl (2ω) depends on the spin Seebeck generation and diffusion of magnons under an inhomogeneous temperature profile, which renders interpretation difficult 21,22 (see SI Section V). Therefore, we focus on V nl (ω) that follows the formula…”