High field ESR measurements of quantum antiferromagnetic chain substances BaCu2(Si1−Ge )2O7

High field ESR measurements of S =1/2 one-dimensional quantum antiferromagnetic (AF) system BaCu 2 (Si 1− x Ge x ) 2 O 7 have been performed using powder samples and pulsed magnetic field. High field electron paramagnetic resonance at 352 GHz and 86 K enabled us to determine the x dependence of g -values even when we used the powder samples. The x dependence will be discussed in connection with the crystal field. Moreover, antiferromagnetic resonances of x =0 and x =1 samples below T N were observed and their frequency–field relations suggest the existence of Dzyaloshinsky–Moriya interaction.