Fig. 2. Microwave absorption processes during in-plane magnetic field sweep.

a When the magnetic field is well below the resonance condition microwaves do not efficiently couple to the uniform FMR mode and there is no microwave absorption. b When the magnetic field becomes close to the resonance condition, strong microwave drive can couple to the uniform mode FMR. In this process two microwave photons are absorbed at ω_MW, giving two uniform mode magnons at ω_MW with k = 0 (white circles) which then decay to a counterpropagating pair of magnons with the same energy, but nonzero-k (solid black circles). The microwave intensity threshold for this process is lowest for the $\overrightarrow{\mathbf{k}}\parallel \overrightarrow{\mathbf{M}}$ spinwave branch. The magnetic field range for which this process occurs is microwave power dependent, resulting in a lineshape change at high microwave powers. c On resonance, the typical microwave excitation of uniform mode precession occurs. d When the magnetic field exceeds the resonance condition there is no microwave absorption due to an absence of available magnon states at the microwave drive frequency.