Probing length-scale separation of thermal and spin currents by nanostructuring YIG

TL;DR

This study investigates how nanostructuring YIG affects thermal and spin currents, revealing different length scales for magnon and phonon transport through measurements of thermal conductivity and spin Seebeck thermopower.

Contribution

It demonstrates that nanostructuring selectively suppresses spin and thermal transport, indicating distinct length scales for magnon and phonon conduction in YIG.

Findings

Nanostructuring reduces thermal conductivity and thermopower.

Magnon transport length scales are larger than phonon scales in YIG.

Long-range magnons are scattered in nanostructured YIG, unlike in single crystals.

Abstract

We have fabricated bulk nanostructured ferrimagnetic materials with different grain sizes by sintering ball-milled Y3Fe5O12 (YIG) nanoparticles and measured the grain-size dependence of the thermal conductivity and spin Seebeck thermopower. The nanostructuring reduces both thermal conductivity and thermopower, but the reduction of the latter was found to be considerably stronger despite the moderate difference in magnetization, which suggests that the length scales of transport of magnons and phonons contributing to the spin Seebeck effect are significantly larger than that of phonons carrying thermal current. This is consistent with the measurements of high-magnetic-field response of the spin Seebeck thermopower and low-temperature thermal conductivity, where the quenching of magnons seen in single-crystalline YIG was not observed in nanostructured YIG due to scattering of long-range low frequency magnons.