MICROWAVE RESONANCE-ABSORPTION IN ANTIFERROMAGNET BI2CUO4

The resonance absorption in Bi2CuO4 single crystals was found in the f requency range 35-80 GHz for H(perpendicular-to)C4 Case and it was abs ent for H(parallel-to)C4 case. The frequency-field dependence for H(pe rpendicular-to)C4 case at 4.2 K is typical for easy-plane antiferromag nets with weak magnetic anisotropy in this plane. In contrast to the s ublattice magnetization of Bi2CuO4 the resonance parameters depend str ongly on the temperature below 20 K. Besides, the resonance field has a considerable jump at TN which ls not typical for second order phase transitions.