Resonant modes in Ising antiferromagnets at the critical magnetic field

Magnetic-resonance properties of Ising antiferromagnets near the critical field Hc are examined. It is found that Hc separates two regimes of completely different behavior. At Hc one line exhibits always vanishing amplitude. It is interesting and somewhat surprising, however, that the vanishing line is the dominant one when the field is varied from Hc in either direction. The vanishing line can be used in magnetic-resonance experiments to determine the critical field Hc. © 1987 The American Physical Society.