Observation of the antiferromagnetic resonance of multi-sublattice modes in KCuF3

We report antiferromagnetic resonance measurements of KCuF3 at various frequencies from 3.8 to 10GHz at 4.2K. A second antiferromagnetic resonance absorption mode is observed in the [100]p direction and equivalent directions, where [ ]p represents an axis in a unit cell of the perovskite structure. Using the eight-sublattice model proposed by Yamada and Kato [J. Phys. Soc. Japan 63 (1994) 289], the numerical calculation for the antiferromagnetic resonance indicates that this second absorption mode comes from one of the resonance modes of the eight-sublattice system.