Environmental effects on big molecule with spin 1/2

The V-15 polyoxovanadate molecule is made of 15 spins 1/2 with antiferromagnetic couplings. It is a low spin/big molecule with spin S=1/2. Contrary to large spins/big molecules of the Mn-12-ac type, V-15 has no energy barrier against spin rotation. Nevertheless, it shows magnetic hysteresis. 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). This behavior is very likely specific to big molecules with low spin. (C) 2000 American Institute of Physics. [S0021-8979(00)31908-9].