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 exte rnal field perpendicular to the easy axis, the susceptibility exhibits a pe culiar peak. We establish that the specific spectral properties of quantum fluctuations give rise to this peak. We predict that this effect takes plac e in real many-spin systems, such as Mn-12 clusters, and can be studied at finite temperatures in real experiments with attainable resolution. For stu dying quantum fluctuations in magnetic molecules, this offers an approach a s an alternative to relaxation rate measurements. (C) 1999 American Institu te of Physics. [S0021-8979(99)39208-2].