GIANT SPINS AND TOPOLOGICAL DECOHERENCE - A HAMILTONIAN APPROACH

We study the topological decoherence, arising from environmental spins , which acts to suppress the quantum coherent behaviour of grain magne tization. It is found that this decoherence mechanism is so effective that even under the most favourable conditions, it will be very diffic ult to see quantum coherent behaviour of grains having a quantum numbe r S greater than approximately O(10). This conclusion does not affect the possibility of seeing tunnelling behaviour for larger grains.