Antiferromagnetic resonance in the double-layered system Rb₃Mn₂Cl₇

Millimetre-wave antiferromagnetic resonance (AFMR) experiments are reported on carefully grown and well characterised single-crystal samples of the double-layered antiferromagnet Rb 3 Mn 2 Cl 7 . The zero-field frequency of the magnetic excitations is found to be 106 GHz. By comparison with the corresponding value in Rb 2 MnCl 4 , this result supports the model in which the anisotropy energy decreases almost proportionally to n in the compounds Rb n+1 Mn n Cl 3n+1 . Some discrepancy with ordinary AFMR theory seems to be observed in the spin-flopped phase.