Field-dependence of magnon decay in yttrium iron garnet thin films

TL;DR

This paper investigates how magnon decay rates in yttrium iron garnet thin films depend on the film thickness and magnetic field, revealing a transition from step-like to linear and power-law behaviors as thickness increases.

Contribution

It demonstrates the threshold field dependence of magnon decay in YIG films and identifies the crossover from two-dimensional to three-dimensional decay behaviors based on film thickness.

Findings

Decay ceases in films thinner than 1 μm.

Decay rate is linear near the threshold field due to symmetry.

Thicker films show multiple decay thresholds and a crossover to 3D behavior.

Abstract

We discuss threshold field-dependence of the decay rate of the uniform magnon mode in yttrium iron garnet (YIG) thin films. We demonstrate that decays must cease to exist in YIG films of thickness less than 1 \mu m, the lengthscale defined by the exchange length. We show that due to the symmetry of the three-magnon coupling the decay rate is linear in \Delta H=(Hc-H) in the vicinity of the threshold field Hc instead of the step-like \Gamma \Theta(\Delta H) expected from the two-dimensional character of magnon excitations in such films. For thicker films, the decay rate should exhibit multiple steps due to thresholds for decays into a sequence of the two-dimensional magnon bands. For yet thicker films, such thresholds merge and crossover to the three-dimensional single-mode behavior: \Gamma |\Delta H|^{3/2}.