Quantum fluctuations in the vicinity of the spin-flop transition in large-spin clusters

If a single-spin possessing an easy-axis anisotropy is subjected to an external field perpendicular to the easy axis, the susceptibility exhibits a peculiar peak. We establish that the specific spectral properties of quantum fluctuations give rise to this peak. We predict that this effect takes place in real many-spin systems, such as Mn-12 clusters, and can be studied at finite temperatures in real experiments with attainable resolution. For studying quantum fluctuations in magnetic molecules, this offers an approach as an alternative to relaxation rate measurements. (C) 1999 American Institute of Physics. [S0021-8979(99)39208-2].