FD-13 Thickness crossover from two- to three-dimensional magnon transport properties

Magnon transport properties are highly dependent on dimensionality. In thermal equilibrium, the magnon number in a 2D system diverges as the effective magnetic field approaches zero, while in a 3D system, it is nearly independent of magnetic anisotropy and external field. Consequently, magnon magnetoresistance in 2D can reach several thousand percent at moderate external field strengths, whereas it is much smaller in 3D systems. For an ultrathin magnetic film composed of only a few monolayers, magnon transport exhibits both 2D and 3D characteristics. We theoretically identify the crossover thickness for both ferromagnetic and antiferromagnetic materials, below which the equilibrium and transport properties of magnons are 2D-like. We find the crossover thickness ranges from one monolayer to several monolayers, depending on the parameters. Our identified crossover thickness can serve as a guideline for determining the film thickness at which a material can be approximately treated as 2D. This work is supported by NSF-ECCS.