Long-range spin Seebeck effect and acoustic spin pumping

Abstract

Imagine that a metallic wire is attached to a part of a large insulator, which itself exhibits no magnetization. It seems impossible for electrons in the wire to register where the wire is positioned on the insulator. Here we found that, using a Ni₈₁Fe₁₉/Pt bilayer wire on an insulating sapphire plate, electrons in the wire recognize their position on the sapphire. Under a temperature gradient in the sapphire, surprisingly, the voltage generated in the Pt layer is shown to reflect the wire position, although the wire is isolated both electrically and magnetically. This non-local voltage is due to the coupling of spins and phonons: the only possible carrier of information in this system. We demonstrate this coupling by directly injecting sound waves, which realizes the acoustic spin pumping. Our finding provides a persuasive answer to the long-range nature of the spin Seebeck effect, and it opens the door to 'acoustic spintronics' in which sound waves are exploited for constructing spin-based devices.

Anomalous Nernst effect in Ir22Mn78/Co20Fe60B20/MgO layers with perpendicular magnetic anisotropy

“…Then, this measurement avoids SSE 19,[40][41][42] and allows a precise determination of the temperature gradient since it is inplane, e.g., by using a thermal camera. 43,44 Previous experiments observed an enhancement of the ANE in stacks containing heavy elements, indicating the relevance of strong spin orbit coupling (SOC) to obtain large Nernst coefficients N ANE , 20,45 e.g., Uchida et al showed that the anomalous Nernst coefficients change from about 0.1 lV/K to 1 lV/K by introducing strong SOC. In this work, we observed an ANE in Ta/IrMn/CoFeB/MgO/Ta structures that is almost 50 times larger than that of a thin film of Ta/ CoFeB/MgO/Ta, i.e., without the IrMn layer.…”

Brillouin light scattering spectra as local temperature sensors for thermal magnons and acoustic phonons

“…This difference between the phonon and magnon temperatures underlies the so called "phonon-magnon drag" that leads to the directional magnon transport or spin current in magnetic insulators and semiconductors. [16][17][18][19] Direct experimental confirmation of this phenomenon is currently lacking most likely due to the small temperature difference between these two temperatures in a sample with a modest temperature gradient. 20 Further improvement in the BLS measurement sensitivity 8 of the magnon and phonon temperatures and the use of a large temperature gradient may help to clarify the fundamental mechanism responsible for thermally driven spin currents.…”

Dynamic spin-current generation in hybrid structures by sound wave

“…The works [42,43] demonstrates that the interaction between conduction electrons and a sound wave field also causes a spin current. It should be here noted that the paper [44] shows experimentally that the response of the spin electron subsystem (analogous to the spin Hall effect), when interacted with the sound wave field, has a resonant nature.…”