INVESTIGATION OF A GAP IN THE AFMR SPECTRUM IN THE QUASI-ONE-DIMENSIONAL HEXAGONAL ANTIFERROMAGNET CSMNBR3

The low-frequency part of the magnetic resonance spectrum of the hexag onal six-sublattice quasi-one-dimensional antiferromagnet CsMnBr3 at t emperatures which are low compared with T-N=8.3 K is investigated expe rimentally. A temperature-dependent gap Delta(T) is found in the spect rum omega(e)(H) of the fewer AFMR branch; this gap is due to the hyper fine interaction of the nuclear spins with the electronic spins of the (Mn-55)(2+) ions. The spectrum of the low-lying resonance frequencies of such a system is calculated taking this interaction into acount in the approximation of fluctuationless spin hydrodynamics for the elect ronic branch of the oscillations. The computational results are in goo d qualitative and satisfactory quantitative agreement with experiment. (C) 1996 American Institute of Physics.