MAGNETIC NEUTRON-SCATTERING IN SINGLE-CRYSTAL BI2CUO4

The spin-wave excitations and the critical behavior of the sublattice magnetization in Bi2CuO4 have been investigated by means of neutron sc attering. The three-dimensional character of the antiferromagnetic ord ering with propagation vector K = (1,0,0) below T(N) = 45.83(8) K is r eflected by the value of the critical exponent beta = 0.352(3). The sp in-wave excitations have been measured along the symmetry directions [ 100] and [001]. The spin-wave dispersion is found to split into two br anches with energy gaps DELTA1 = 2.1 meV and DELTA2 = 3.4 meV at the z one center. The data analysis is based on an S=1/2 spin Hamiltonian of tetragonal symmetry with anisotropic bilinear exchange including a fo ur-site exchange interaction term.