11B-NMR study on Shastry-Sutherland system TbB4

11B-NMR experiments were performed in high magnetic fields applied along a-axis up to 17.5T to investigate the field-induced magnetic phase transitions and the magnetic structure in high magnetic fields microscopically for the single crystalline TbB4, Shastry-Sutherland-type frustrated antiferromagnet. It was found that the field-swept 11B-NMR spectra observed at low magnetic field changes drastically at HC = 15.9 T, where the magnetization jump occurs. Based on a simple model of four-spin cluster and the classical dipole-dipole interaction, we have calculated NMR spectra, which qualitatively reproduced the observation below HC but the one above HC showed discrepancy.