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

TL;DR

This study demonstrates anisotropic magnon spin transport in ultra-thin spinel ferrite films, revealing longer spin diffusion lengths along easy axes due to exchange stiffness anisotropy, challenging previous energy-based explanations.

Contribution

It provides experimental evidence of anisotropic magnon transport linked to exchange stiffness anisotropy in ultra-thin ferrite films, a novel insight in spintronics.

Findings

Spin diffusion length exceeds 0.8 μm at room temperature.

Spin diffusion length is 30% longer along easy axes.

Exchange stiffness anisotropy explains the observed transport behavior.

Abstract

We report measurements of magnon spin transport in a spinel ferrite, magnesium aluminum ferrite $\mathrm{MgAl_{0.5}Fe_{1.5}O_4}$ (MAFO), which has a substantial in-plane four-fold magnetic anisotropy. We observe spin diffusion lengths $> 0.8$ $\mathrm{\mu m}$ at room temperature in 6 nm films, with spin diffusion length 30% longer along the easy axes compared to the hard axes. The sign of this difference is opposite to the effects just of anisotropy in the magnetic energy for a uniform magnetic state. We suggest instead that accounting for anisotropy in exchange stiffness is necessary to explain these results.