High frequency EPR on dilute solutions of the single molecule magnet Ni₄

Dilute frozen solutions of the single molecule magnet Ni₄ (S=4) have been studied using 130 GHz electron paramagnetic resonance (EPR). Despite the random orientation of the molecules, well defined EPR absorption peaks are observed due to the strong variation of the splittings between the different spin states on magnetic field. Temperature dependent studies above 4 K and comparison with simulations enable identification of the spin transitions and determination of the Hamiltonian parameters. The latter are found to be close to those of Ni4 single crystals. No echo was detected from Ni4 in pulsed experiments, which sets an upper bound of about 50 ns on the spin coherence time.