Frequency Dependence of Resonance Field of One-Dimensional Heisenberg Antiferromagnet KCuF₃

The frequency dependence of the in-plane angular change of the antiferromagnetic resonance (AFMR) field of KCuF₃ is systematically measured at frequencies ranging from 3.8 to 10.6GHz at 4.2K. The effect of inequivalent g-tensors is found to gradually diminish with decreasing the frequency, and completely vanish when the frequency is decreased to the lower-frequency branch of C-band, while the effect of the effective anisotropy field is significantly enhanced with decreasing the frequency. The calculated AFMR field H_res based on the eight-sublattice model proposed by Yamada and Kato J. Phys. Soc. Jpn. 63(1994)289 is in good agreement with the experimental data.