MAGNETIC ORDER OF S=1 2 SPILLS ON THE FCC LATTICE AT ZERO-TEMPERATURECALCULATED BY EXACT DIAGONALIZATION/

The magnetic order of s = 1/2 spins with Heisenberg couplings on the F CC lattice at T = 0 has been probed by examining the ground state of f inite clusters with periodic boundary conditions, for different ratios of the nearest and next-nearest-neighbour couplings, J(1) and J(2). R esults for 32 spins show that the type of antiferromagnetic order is i ndependent of the external held, in agreement with recent experimental results on nuclear magnetic order in silver. Results of calculations on 64 spins in a high field implies that the zero-held phase diagram i n the (J(1), J(2)) plane is close to the classical predictions. (C) 19 98 Elsevier Science B.V. All rights reserved.