Finite segments, “free spins” and random exchange in spin S=1 quasi one-dimensional antiferromagnets

Abstract

Magnetic susceptibility of representative examples of S=1 Heisenberg antiferromagnetic chains, AgVP 2S 6 and NENP, has a divergent low temperature contribution, in spite of the fact that the bulk susceptibility should vanish due to the presence of the Haldane gap. The divergence follows a power law T -α with α≈0.6 that is quite different from free spin paramagnetism. We propose that this contribution is due to finite segments that weakly interact to form a Random Exchange system.