Non-adiabatic Landau-Zener transitions in low-spin molecular magnet V15

The V-15 polyoxovanadate molecule is made of 15 spins: with antiferromagnetic couplings. It belongs to the class of molecules with very large Hilbert space dimension (2(15) in V-15, 10(8) in Mn-12-AC). It is a low spin/large molecule with spin S = 1/2 Contrary to large spins/large molecules of the Mn-12-AC type, V-15 has no energy barrier against spin rotation. Magnetization measurements have been performed and despite the absence of a barrier, magnetic hysteresis is observed over a timescale of several seconds. This new phenomenon characterized by a "butterfly" hysteresis loop is due to the effect of the environment on the quantum rotation of the entangled 15 spins of the molecule, in which the phonon density of states is not at its equilibrium (phonon bottleneck). (C) 2000 Elsevier Science B.V. All rights reserved.