We observed a field-induced staggered magnetization in the 2D frustrated dimer-singlet spin system SrCu2(BO3)2 by 11B NMR, from which the magnitudes of the intradimer Dzyaloshinsky-Moriya interaction and the staggered g-tensor were determined. These anisotropic interactions cause singlet-triplet mixing and eliminate a quantum phase transition at the expected critical field Hc for gap closing. They also provide a quantitative account for some puzzling phenomena such as the onset of a uniform magnetization below the and the persistence of the excitation gap above Hc. The gap was accurately determined from the activation energy of the nuclear relaxation rate.
@article{arxiv.cond-mat/0404482,
title = {Field-Induced Effects of Anisotropic Magnetic Interactions in SrCu2(BO3)2},
author = {K. Kodama and S. Miyahara and M. Takigawa and M. Horvatic and C. Berthier and F. Mila and H. Kageyama and Y. Ueda},
journal= {arXiv preprint arXiv:cond-mat/0404482},
year = {2009}
}