UC San Diego

The synthesis and study of magnetic nanostructures is of both intense scientific and technological interest. A single-molecule magnet (SMM) is a molecular nanomagnet that can be magnetized as a result of having a large spin ground state that experiences appreciable magnetoanisotropy, which leads to a thermodynamic barrier between "spin-up" and "spin-down" orientations. The monodisperse nature (same size, shape and anisotropy) of SMMs permits detailed studies of the magnetization and quantum dynamics of nanomagnets. The discovery of SMMs permitted, for the first time, detailed study of quantum effects associated with nanomagnets. The magnetic and quantum properties of these complexes is heavily dictated by molecular and crystal symmetry, and paramount to employing these systems as devices is a need to thoroughly understand and control environmental factors that govern their magnetization and quantum dynamics. To some extent this can be achieved by changing or eliminating co- crystallized solvate molecules and interchanging coordinated peripheral ligands. Magnetic and thermodynamic studies were carried out on a high symmetry system that exhibits a large spin ground state (S =51/2), a preferred orientation in an applied magnetic field, and slow magnetization relaxation dynamics. Strong competing magnetic exchange coupling between paramagnetic copper and manganese ions, in conjunction with high symmetry, gives rise to appreciable spin-frustration and geometric- frustration. These correlated effects lead to slow magnetization relaxation behavior. Detailed magnetization and thermodynamic studies were performed on a series of tetranuclear nickel complexes that exhibit fast magnetization tunneling and magnetic ordering. Magnetic ordering is a collective process that should drastically suppress or terminate quantum tunneling processes. It is revealed that even in an ordered state, the molecules within the crystal lattice act as single domains, thus, molecules quickly switch between magnetic ordering and single-domain quantum tunneling. A series/family of multifunctional tetranuclear manganese SMMs (magnetic and photoluminescent) were synthesized that systematically differ in co-crystallized solvate molecules and peripheral organic ligands to study magneto-structural correlation effects and quantum tunneling of magnetization. The goal is to couple emissive excited states to the magnetic moment of the SMM, which may allow, for the first time, detailed study of quantum dynamics on a 10⁻⁹-10⁻¹²s time scale