Fluctuation inducing fractional magnetization behavior on the Shastry–Sutherland lattice

Abstract

We investigate disorder effects using Callen identities on the Ising model with anti-ferromagnetic (AF) spin couplings on the Shastry–Sutherland (SS) lattice using Monte Carlo simulation. The field-dependent magnetization curve of the Ising model on the SS lattice without disorder consists of only one main magnetization plateau with the fractional value m∕ms=1∕3 (the saturation magnetization ms). In the inclusion of disorder, the fascinating sequence of magnetization plateau is surprisingly found with fractional values depending on the fluctuation probability of the AF exchange interaction between nearest-neighbor (NN) and next-nearest-neighbor (NNN) sites. We explain successfully an intimate relation between the phase diagram of ground states of the standard SS model and the appearance of multi-steps in the field-dependent magnetization curve which is experimentally observed in many compounds as SrCu2(BO3) and the rare-earth tetraborides RB4 (R = Tm, Ho, Er).