  The linewidth of antiferromagnetic resonance (AFMR) is found to be
significantly broader than that of ferromagnetic resonance (FMR), even when the
intrinsic Gilbert damping parameter is the same for both systems. We
investigate the origin of this enhanced damping rate in AFMR by studying a
bipartite magnet model. Through analytical calculations and numerical
simulations, we present three perspectives on understanding this linewidth
broadening in AFMR: i) The non-dissipative Heisenberg exchange interaction
develops a damping-like component in the presence of Gilbert damping, ii) The
transverse component of the exchange coupling reduces the AFMR frequency,
thereby increasing the damping rate, and iii) The antiferromagnetic eigenmode
exhibits characteristics of a two-mode squeezed state, which is inherently
linked to an enhanced damping rate. Our findings provide a comprehensive
understanding of the complex dynamics governing magnetic dissipation in
antiferromagnet and offer insights into the experimentally observed broadened
linewidths in AFMR spectra.
