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VOLUME 63 (1996) | ISSUE 9 | PAGE 688
Macroscopic quantum tunneling in small magnetic particles
Macroscopic quantum tunneling of magnetization in small antiferromagnetic clusters is studied for the spin-1/2 anisotropic (Jz Ξ J, Jx ™ Jy Ξ Jxy) Heisenberg model employing both perturbation theory and exact numerical diagonalization technique. Splitting between the two lowest levels due to the lifting of degeneracy between them (occurring for Jxv — 0) by the in-plane exchange (Jxy *f 0) is found to occur in the iV/2-th order of the perturbation theory. The tunneling is absent in systems with odd number of sites where all levels are doubly degenerate in zero magnetic field. PACS: 03.65.Sq, 75.10.Jm, 75.30.Gw, 75.60Jp