Environmental effects on big molecule with spin 1/2

The V-15 polyoxovanadate molecule is made of 15 spins 1/2 with antiferromag netic 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 ne w phenomenon characterized by a "butterfly" hysteresis loop is due to the e ffect 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 equili brium (phonon bottleneck). This behavior is very likely specific to big mol ecules with low spin. (C) 2000 American Institute of Physics. [S0021-8979(0 0)31908-9].