The Effects of Dzyaloshinsky-Moriya Interaction in the Orthogonal Dimer Heisenberg Model for SrCu2(BO3)2

Abstract

The new two-dimensional spin-gap system SiCu 2 (BO 3 ) 2 shows unique physical properties because of its low-dimensionality character and of strong quantum fluctuations due to frustration. The magnetic properties of the material, e.g. dirner singlet ground state, an almost localized triplet and magnetization plateaus, are well described by a spin-1/2 antiferromagnetic Heisenberg model on the orthogonal dimer lattice. However, in the presence of an external magnetic field, unusual magnetic properties, which cannot be explained by the Heisenberg model alone, have been observed in several experiments: (1) a field induced staggered moment, (2) the persistence of an excitation gap at around the critical field, and (3) a finite magnetization below the critical field. We include intra- and inter-dimer Dzyaloshinsky-Moriya interactions and the staggered gyromagnetic tensors in the orthogonal dimer Heisenberg model, and show that these unusual behaviors with the external field in the z direction can be well described with physically reasonable values of the parameters.