Absence of collective effects in Heisenberg systems with localized magnetic moments

Abstract

Existence of collective effects in magnetic coupling in ionic solids is studied by mapping spin eigenstates of the Heisenberg and exact nonrelativistic Hamiltonians on cluster models representing (Formula presented), (Formula presented), NiO, and (Formula presented). Ab initio techniques are used to estimate the Heisenberg constant (Formula presented). For clusters with two magnetic centers, the values obtained are about the same for models having more magnetic centers. The absence of collective effects in (Formula presented) strongly suggests that magnetic interactions in this kind of ionic solids are genuinely local and entangle only the two magnetic centers involved. © 1997 The American Physical Society.