ONE-DIMENSIONAL FRUSTRATED HEISENBERG-ANTIFERROMAGNET OF SPIN 1/2 IN A STRONG MAGNETIC-FIELD

The properties of the one-dimensional antiferromagnet of spin 1/2 in a strong magnetic field h with nearest- and next-nearest-neighbor interactions are studied in terms of the equivalent Bose-gas problem. We find that below the first critical field h(cu) a phase with a gap in the elementary excitation spectrum and corresponding plateau in the magnetization curve should exist due to the two-particle attraction in the vicinity of the commensurate wave number p0u = pi. In the interval between the first and second critical fields h(cu) < h < h(cf), the system behaves as the one-dimensional Bose gas with particle repulsion and the magnetization has a typical square-root dependence on field.