Magnetic and microwave studies of high-spin states of single-molecule magnet Ni4

Quantum tunneling of the magnetization in a single-molecule magnet has been studied in experiments that combine microwave spectroscopy (10–50 GHz) with low temperature high sensitivity micro-Hall effect magnetometry (T = 0.4 K). This method enables the monitoring of spin-state populations in the presence of microwave radiation and a direct measure of the energy splitting between low lying high-spin states. We present results that show the level repulsion between such states as a function of magnetic field in the SMMNi4 (S = 4), which clearly indicates the formation of high-spin superposition states. The absorption linewidths provide a lower bound on the transverse relaxation time (s2) or decoherence time of these superposition states of 0.5 ns. Studies as a function of microwave power and magnetic field sweep rate suggest that the energy relaxation rate decreases with increasing longitudinal field and energy splitting between states. 2005 Elsevier Ltd. All rights reserved.