Many-spin effects and tunneling properties of magnetic molecules

Spin tunneling in molecular magnets has attracted much attention, however t heoretical considerations of this phenomenon up to now have not taken into account the many-spin nature of molecular magnets. We present, to our knowl edge, the first successful attempt of a realistic calculation of tunneling splittings for Mn-12 molecules, thus achieving a quantitatively accurate ma ny-spin description of a real molecular magnet in the energy interval rangi ng from about 100 K down to 10(-12) K. Comparison with the results of the s tandard single-spin model shows that many-spin effects affect the tunneling splittings considerably. The values of ground state splitting given by sin gle-spin and many-spin models differ from each other by a factor of 5. (C) 2000 American Institute of Physics. [S0021-8979(00)66308-9].