High-field ESR study on frustrated spin chain system KCu5V3O13

High-field ESR technique has been applied to the novel frustrated spin chain system KCu5V3O13, to reveal the peculiar ground state proposed by the previous results of the magnetic susceptibility and the magnetization measurements. We successfully observed the antiferromagnetic resonance with the easy axis type anisotropy below 7 K . In addition, small shifts of the resonance field probably due to the re-arrangements of spin configuration in the ordered phase were also observed at about 4 K in the detailed temperature dependence measurements. This result confirmed the observation of double peaks at 3.9 and 7 K in the specific heat measurements performed in advance to the high-field ESR measurements. We will discuss about the ground state of KCu5V3O13 based on these results together with those obtained in the KMgCu4V3O13, where no antiferromagnetic resonance was observed.