Magnon transport in two-dimensional magnets

Magnon mediated transport through three-dimensional (3D) magnetic insulating thin films

such as Yttrium Iron Garnet has been a recent topic of interest in the field of spintronics.

However, the typically low magnon density in these 3D films results in reduced magnon

conductance. In this work, we investigate the theoretical aspects of magnon conductance of

two-dimensional (2D) materials, where an enhanced magnon density offers promise. We

calculate the magnon scattering rate and conductivity, accounting for magnon-magnon

interactions in a pristine, two-dimensional ferromagnetic material with an easy-axis

anisotropy. Furthermore, we establish their correlation with parameters like external field

strength, field orientation, and temperature. Our findings indicate that conductivity faces

significant suppression for fields which are neither parallel nor perpendicular to the easy axis.

This is attributed to non-magnon conserving processes that emerge at lower orders in the

Holstein-Primakoff expansion. Drawing from our theoretical framework, when applied to an

experimental setup similar to that of Wei et al. [1], where two Pt bars rest atop a 2D magnet,

we predict the attenuation length of magnon current decay can be controlled by the

direction and the magnitude of the external magnetic field.

[1] X. Y. Wei, O. A. Santos, C. H. Sumba Lusero, G. E. W. Bauer, J. Ben Youssef, and B. J. Van Wees, Nat.

Mater. 21, 1352 (2022).