  The Self-Consistent Harmonic Approximation (SCHA) has demonstrated efficacy
in discerning phase transitions and, more recently, in elucidating coherent
phenomena within ferromagnetic systems. However, a notable gap in understanding
arises when extending this framework to antiferromagnetic models. In this
investigation, we employ the SCHA formalism to conduct an in-depth exploration
of the Antiferromagnetic Resonance (AFMR) within both Antiferromagnetic (AF)
and Spin-Flop (SF) phases. Our analysis includes thermodynamic considerations
from both semiclassical and quantum perspectives, with comparisons drawn
against contemporary experimental and theoretical data. By incorporating a
treatment utilizing coherent states, we investigate the dynamics of
magnetization precession, a fundamental aspect in comprehending various
spintronic experiments. Notably, the SCHA demonstrates excellent agreement with
existing literature, showcasing its simplicity and efficiency in describing
AFMR characteristics, even close to the transition temperature.
