MAGNETIC-PROPERTIES OF HUBBARD CLUSTERS - NONCOLLINEAR SPINS IN N-ATOM CLUSTERS

The ground-state magnetic properties of clusters with N-atomic sites a re studied by solving the single-band Hubbard Hamiltonian in the unres tricted Hartree-Fock, approximation. Three-dimensional arrangements of spins are considered in the solution. Results for stability and magne tic order, as a function of the Coulomb interaction strength U/t, and number of electrons nu, are presented for all the clusters with N = 3, 4, and for the set of N = 13 fcc-, hcp-, icosahedral-, and bcc-like c lusters. In most cases, for band fillings (nu) close to half-band \nu/ N-1\ less than or equal to 0.2-0.4, it is found that the antiferromagn eticlike noncollinear spin solutions yield the smallest energy for U/t larger than a critical value (0 < (U/t)(c) less than or equal to 6). (C) 1997 American Institute of Physics.