Experimental Examination of Chain-Dimer Model in Ca1-xCuO2(x=0.164) by High Field ESR Measurements

Intensive high-field ESR studies have been performed to investigate the peculiar ground state of a quasi-one dimensional cupric oxide Ca 1- x CuO 2 ( x =0.164), to which a two-sublattice model (chain-dimer model) composed of a Heisenberg antiferromagnetic chain and dimer state with low spin density is proposed from the results of magnetic susceptibility and specific heat measurements. Using the powder sample and high frequency sources from 60 to 490 GHz, we observed antiferromagnetic resonance mode with a typical frequency–field relation of the easy-axis type at 1.8 K. Moreover, weak ESR signals are also observed in the ordered state. From the analysis of the integrated intensity for those weak signals, it is found that the dimer model reproduces the temperature dependent behaviors quite well. These results support the chain-dimer model from the microscopic point of view.