Jon Lawrence

Synthesis and characterisation of a Ni(4) single-molecule magnet with S(4) symmetry

[Ni4Cl4(HL)4] () {H2L=HN(CH2CH2OH)2} has S4 symmetry and crystallises in the tetragonal space group I4(1)/a. Two exchange couplings are observed between the four Ni(II) centres, with J1=7.29 cm(-1) and J2=-2.08 cm(-1), leading to an S=4 ground state. The Ni4 complex shows the onset of frequency dependent signals in the out-of-phase ac susceptibility below 3 K. In single-crystal measurements carried out using a micro-SQUID, hysteresis loops are observed below 0.5 K, confirming that shows slow relaxation of magnetisation. The loops are temperature dependent but only weakly sweep rate dependent due to the presence of small intermolecular interactions, which hinder quantum tunnelling. This exchange bias between Ni4 molecules is also seen in high-frequency high-field EPR measurements, which give the parameters D=-0.75 cm(-1), B4 degrees=-6.7x10(-5) cm(-1) and gz=2.275.

Origin of the fast magnetization tunneling in the single-molecule magnet [Ni(hmp)(t-BuEtOH)Cl]4

We present high-frequency angle-dependent EPR data for crystals of [NixZn1−x(hmp)(t‐BuEtOH)Cl]4 (x=1 and 0.02). The x=1 complex behaves as a single-molecule magnet at low temperatures, displaying hysteresis and exceptionally fast magnetization tunneling. We show that this behavior is related to a fourth-order transverse crystal-field interaction, which produces a significant tunnel splitting (∼10MHz) of the ground state of this S=4 system. The magnitude of the fourth-order anisotropy, and the dominant axial term (D), can be related to the single-ion interactions (Di and Ei) at the individual NiII sites, as determined for the x=0.02 crystals.

Magnetic Quantum Tunneling in a Mn12 Single‐Molecule Magnet Measured With High Frequency Electron Paramagnetic Resonance

The low temperature spin dynamics of the single‐molecule magnet [Mn12O12(CH3COOH)16(H2O)4]. 2CH3COOH⋅4H2O, hereafter Mn12Ac, were studied using High Frequency Electron Paramagnetic Resonance (HFEPR) in order to demonstrate magnetic quantum tunneling between resonant spin projection states. We prepare the spins such that they populate only one side of the axial potential energy barrier. Using a magnetic field we cause tunneling between resonant energy states. We then use HFEPR to monitor the populations on each side of the potential energy barrier. We can estimate the tunneling relaxation time between spin projection states by plotting the area of an EPR peak as a function of wait time at a resonance field. This technique provides an alternative method to magnetometry experiments for measuring spin relaxation dynamics.